main/postmarketos-mkinitfs: Support initramfs compressions other than gzip

The postmarketos initramfs is larger than android initramfs. This causes problems on some devices like htc-ace that have a very small boot partition (4MB in htc-ace). I've been able to make the boot image small enough to fit by compressing initramfs using lzma.

With this change it should be possible to change the compression in deviceinfo like this: deviceinfo_initramfs_compression='lzma' or even deviceinfo_initramfs_compression='lzma -9'

When no option is specified it defaults to 'gzip -1'.

I'm not very experienced in shell scripting so I'm not sure if this is the best way to do it. I've also added dependencies to compression utilities for all possible initramfs compression algorithms.

main/postmarketos-mkinitfs/APKBUILD

 pkgname=postmarketos-mkinitfs
-pkgver=0.7.6
+pkgver=0.7.7
 pkgrel=0
 pkgdesc="Tool to generate initramfs images for postmarketOS"
 url="https://postmarketos.org"
 # multipath-tools: kpartx
 depends="busybox-extras lddtree cryptsetup kmod multipath-tools postmarketos-splash
-	device-mapper parted e2fsprogs e2fsprogs-extra osk-sdl charging-sdl triggerhappy"
+	device-mapper parted e2fsprogs e2fsprogs-extra osk-sdl charging-sdl triggerhappy xz bzip2 lz4"
 triggers="$pkgname.trigger=/etc/postmarketos-mkinitfs/hooks:/usr/share/kernel/*"
 source="init.sh.in init_functions.sh mkinitfs.sh"
 arch="noarch"
@@ -26,4 +26,4 @@ package() {
 
 sha512sums="2479b08e48450f7d46c83b1117d0d81edf26dad8f2107e2ae1b10689f1b063c38181be735957ec1a16392302815355ca879ab71fc28d084e075f490cb2ac42b5  init.sh.in
 e4972ba261a72daba0d1f2fad425a3df082e18263a716746005f31a5cae313d66c168e09cd1bd0af3cee6a97bdb4b329ee3a8d03381a5b104fb39476bdcc7938  init_functions.sh
-5ad842720e7f322bab43aa585103f5bd7e4b11e2e8cce553d406123e4379c160a1b8d7ed1b6aae75b040b2df309c105c412826a8467d552576d6d9ac1f6792ab  mkinitfs.sh"
+2de44d5109be98aa2476640cb298b5dcb8366b8104af188768634ea3a0eeea9b7cc71e94f2f1ce09cd3b8200b7d4515719905ecf1301fcce94ded34f36e849e1  mkinitfs.sh"