main/linux-vanilla: fix /boot/dtbs directory

install dtbs under /boot/dtbs instead of /boot/dtbs/$_abi_release
so the u-boot can find it without need to fix/change DEVICETREEDIR
in extlinux.conf on every kernel upgrade

This will work until we made versioned kernel upgrade and preserve
previous kernel version on upgrade

main/linux-vanilla/APKBUILD

@@ -7,7 +7,7 @@ case $pkgver in
 	*.*.*)	_kernver=${pkgver%.*};;
 	*.*) _kernver=$pkgver;;
 esac
-pkgrel=0
+pkgrel=1
 pkgdesc="Linux vanilla kernel"
 url="http://kernel.org"
 depends="mkinitfs"
@@ -131,7 +131,7 @@ _package() {
 	local _install
 	case "$CARCH" in
 	arm*)
-		local _dtbdir="$_outdir"/boot/dtbs/${_abi_release}
+		local _dtbdir="$_outdir"/boot/dtbs
 		mkdir -p "$_dtbdir"
 		for i in arch/arm/boot/dts/*.dtb ; do
 			install -m644 "$i" "$_dtbdir"