device-postmarketos-trailblazer: add linux-postmarketos-mainline subpackage

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

device/testing/device-postmarketos-trailblazer/APKBUILD

@@ -4,7 +4,7 @@ maintainer="Casey Connolly <kcxt@postmarketos.org>"
 pkgname=device-postmarketos-trailblazer
 pkgdesc="postmarketOS Trailblazer generic ARM64"
 pkgver=18
-pkgrel=0
+pkgrel=1
 url="https://postmarketos.org"
 license="MIT"
 arch="aarch64"
@@ -36,6 +36,7 @@ install="$pkgname.pre-upgrade"
 makedepends="devicepkg-dev"
 subpackages="
 	$pkgname-kernel-next:kernel_next
+	$pkgname-kernel-mainline:kernel_mainline
 	$pkgname-kernel-lts:kernel_lts
 	$pkgname-kernel-stable:kernel_stable
 	$pkgname-kernel-postmarketos-qcom-laptop:kernel_postmarketos_qcom_laptop
@@ -60,6 +61,12 @@ kernel_next() {
 	devicepkg_subpackage_kernel $startdir $pkgname $subpkgname
 }
 
+kernel_mainline() {
+	pkgdesc="Mainline postmarketOS kernel (linux-postmarketos-mainline)"
+	depends="linux-postmarketos-mainline"
+	devicepkg_subpackage_kernel $startdir $pkgname $subpkgname
+}
+
 kernel_lts() {
 	pkgdesc="Long term support (LTS) kernel from Alpine Linux (linux-lts)"
 	depends="linux-lts"