main/postmarketos-ondev: upgrade to 0.3.2 (MR 1780)

The calamares module and branding was made distro-agnostic and moved to
calamares-extensions.git. A new "make install" target inside
postmarketos-ondev.git installs all files, so we need less logic in the
APKBUILD.

Replace lightdm with tinydm. Add xset dependency to disable screen
blanking.