Initial PINE A64-LTS support

Here's my WIP branch for the PINE A64-LTS, mainline u-boot crashes before starting the kernel:

U-Boot SPL 2018.05 (Sep 08 2018 - 15:35:14 +0000)
DRAM: 0 MiB
### ERROR ### Please RESET the board ###

This branch also depends on https://gitlab.com/postmarketOS/pmbootstrap/merge_requests/1693

device/device-pine-a64lts/APKBUILD

+# Reference: <https://postmarketos.org/devicepkg>
+pkgname="device-pine-a64lts"
+pkgdesc="PINE A64-LTS"
+pkgver=0.1
+pkgrel=0
+url="https://postmarketos.org"
+license="MIT"
+arch="noarch"
+options="!check"
+depends="postmarketos-base linux-pine-a64lts mesa-dri-swrast u-boot-pine64 uboot-tools"
+makedepends="devicepkg-dev"
+source="
+	deviceinfo
+	uboot-script.cmd
+"
+
+build() {
+	devicepkg_build $startdir $pkgname
+	mkimage -A arm -O linux -T script -C none -a 0 -e 0 -n postmarketos -d "$srcdir/uboot-script.cmd" "$srcdir/boot.scr"
+}
+
+package() {
+	devicepkg_package $startdir $pkgname
+	install -D -m644 "$srcdir"/boot.scr \
+		"$pkgdir"/boot/boot.scr
+
+}
+
+sha512sums="d320598d0c265344890b72ce2ffe34741765d5606ddaefa0cc621b7116b28d34220523350b69c4c9cb8780ec0c918e36b80bd247720a4d079c97d740d84ebaff  deviceinfo
+fc71acf937691b09f2ac9b8cd724af245555c90fdff6a1fd0e64c0cad04cfc0b46ff5dec61b3ff42e6b076b02e5cf2518089c54340c35a91c0b2b88731826492  uboot-script.cmd"