device-qemu-aarch64: add linux-postmarketos-mainline subpackage

Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7398>

device/main/device-qemu-aarch64/APKBUILD

@@ -3,7 +3,7 @@
 maintainer="Oliver Smith <ollieparanoid@postmarketos.org>"
 pkgname=device-qemu-aarch64
 pkgver=15
-pkgrel=0
+pkgrel=1
 pkgdesc="Simulated device in QEMU (aarch64)"
 url="https://postmarketos.org"
 arch="aarch64"
@@ -18,6 +18,7 @@ subpackages="
 	$pkgname-kernel-lts:kernel_lts
 	$pkgname-kernel-virt:kernel_virt
 	$pkgname-kernel-stable:kernel_stable
+	$pkgname-kernel-mainline:kernel_mainline
 	$pkgname-pmtest
 	"
 
@@ -74,6 +75,12 @@ kernel_stable() {
 	devicepkg_subpackage_kernel $startdir $pkgname $subpkgname
 }
 
+kernel_mainline() {
+	pkgdesc="postmarketOS Mainline kernel"
+	depends="linux-postmarketos-mainline linux-firmware-none"
+	devicepkg_subpackage_kernel $startdir $pkgname $subpkgname
+}
+
 pmtest() {
 	install_if="$pkgname=$pkgver-r$pkgrel postmarketos-mkinitfs-hook-ci"
 	depends="postmarketos-test-unl0kr"