linux-postmarketos-qcom-sm6125: new aport

This commit adds a package for the sm6125-mainline kernel fork. As of
now it uses kernel version 5.18_rc4, pulled from torvalds/linux.
You can find the repository on https://gitlab.com/sm6125-mainline/linux

linux-postmarketos-qcom-sm6125: Change commit to master branch

I'm planning to organize the sm6125-mainline project with the following
branch scheme:

- master: Stable release, commits here will be sent to LKML
- upstream: For pulling changes from torvalds/linux, testing and fixing
  prior to merging into master
- Any other branches will be used to implement new features to master

This commit switches the previously used commit in favor of the master branch.

linux-postmarketos-qcom-sm6125: Fixed checksums

linux-postmarketos-qcom-sm6125: Metadata adjustments

To be more exact, this commit:
- Changes the package version from 5.18.0 to 5.18_rc4, which is the
  current kernel version
- Specifies the location of the kernel config base

device/testing/linux-postmarketos-qcom-sm6125/APKBUILD

+# Reference: <https://postmarketos.org/vendorkernel>
+# Kernel config based on: arch/arm64/configs/defconfig
+
+pkgname=linux-postmarketos-qcom-sm6125
+pkgver=5.18_rc4
+pkgrel=0
+pkgdesc="Mainline Kernel fork for SM6125 devices"
+arch="aarch64"
+_carch="arm64"
+_flavor="postmarketos-qcom-sm6125"
+url="https://kernel.org"
+license="GPL-2.0-only"
+options="!strip !check !tracedeps pmb:cross-native"
+makedepends="
+	bash
+	bc
+	bison
+	devicepkg-dev
+	flex
+	openssl-dev
+	perl
+"
+
+# Source
+_repository="linux"
+_commit="master"
+_config="config-$_flavor.$arch"
+source="
+	$pkgname-$_commit.tar.gz::https://gitlab.com/sm6125-mainline/$_repository/-/archive/$_commit.tar.gz
+	$_config
+"
+builddir="$srcdir/$_repository-$_commit"
+
+
+prepare() {
+	default_prepare
+	cp "$srcdir/config-$_flavor.$arch" .config
+}
+
+build() {
+	unset LDFLAGS
+	make ARCH="$_carch" CC="${CC:-gcc}" \
+		KBUILD_BUILD_VERSION="$((pkgrel + 1 ))-$_flavor"
+}
+
+package() {
+	mkdir -p "$pkgdir"/boot
+
+	install -Dm644 "$builddir/arch/$_carch/boot/Image.gz" \
+		"$pkgdir/boot/vmlinuz"
+
+	make modules_install dtbs_install \
+		ARCH="$_carch" \
+		INSTALL_PATH="$pkgdir"/boot/ \
+		INSTALL_MOD_PATH="$pkgdir" \
+		INSTALL_MOD_STRIP=1 \
+		INSTALL_DTBS_PATH="$pkgdir"/usr/share/dtb
+	rm -f "$pkgdir"/lib/modules/*/build "$pkgdir"/lib/modules/*/source
+
+	install -D "$builddir"/include/config/kernel.release \
+		"$pkgdir"/usr/share/kernel/$_flavor/kernel.release
+}
+
+
+sha512sums="
+1015de59e6e60619149f9931f9c283954d6fb7ce06ff75f8aaa69c13c934a3e8e504d0f37702c2032d72e6ca871e33416f16447532d2626a6a0ade42b7160819  linux-postmarketos-qcom-sm6125-master.tar.gz
+695be42583078511a180cc2bc36f70a038ff1a3c5e81e084c70ee9341936159ee695884d3e43e5afd6be717ab35e3445ac577c04f4847670040d0c6ab28651fa  config-postmarketos-qcom-sm6125.aarch64
+"