Various pkgver fixups

temp/mesa-purism-gc7000: use _commit variable instead of _sha the rest: use _git pkgvers for packages that use a specific git commit

$ git grep "_commit=\"" | grep -v 'device/' | grep -v 'firmware/' | cut -d':' -f1 | uniq > commit-packages
$ git grep "pkgver=" | grep -v 'firmware/' | grep "_git" | cut -d':' -f1 | uniq > git-packages
$ diff -u commit-packages git-packages

The remaining packages:

• main/android-mkdtimg: the source isn't even upstream and it's only used for google-crosshatch mainline
• main/libsignon-glib: false positive
• main/linux-postmarketos-qcom: pkgver doesn't really matter there imo