linux-lenovo-21bx: upgrade to 6.12

To help with testing: mrtest add 5681. I intend to update this branch when new RCs are out so that it's easy for me/others to test, then merge when 6.12 is released.

device/community/linux-lenovo-21bx/APKBUILD

@@ -28,7 +28,6 @@ makedepends="
 	openssl-dev
 	perl
 	python3
-	postmarketos-installkernel
 "
 
 # Source
@@ -53,17 +52,20 @@ build() {
 }
 
 package() {
-	mkdir -p "$pkgdir"/boot
-	make zinstall modules_install dtbs_install \
+	install -Dm644 "$builddir/arch/$_carch/boot/vmlinuz.efi" \
+			"$pkgdir/boot/linux.efi"
+
+	make modules_install dtbs_install \
 		ARCH="$_carch" \
-		INSTALL_PATH="$pkgdir"/boot \
+		INSTALL_PATH="$pkgdir"/boot/ \
 		INSTALL_MOD_PATH="$pkgdir" \
 		INSTALL_MOD_STRIP=1 \
 		INSTALL_DTBS_PATH="$pkgdir"/boot/dtbs
+
 	rm -f "$pkgdir"/lib/modules/*/build "$pkgdir"/lib/modules/*/source
 
 	install -D "$builddir"/include/config/kernel.release \
-		"$pkgdir"/usr/share/kernel/$_flavor/kernel.release
+		"$pkgdir"/usr/share/kernel/next-"$_nextver"/kernel.rele
 }
 
 sha512sums="