we need add a dependency that provides /bin/sh

Commit 3b5707d3 moved ghc from
testing to community, but bootstrap.sh was not updated.

Strictly the 'efi' folder is not needed since it's in the efi.img.
However, converting .iso to USB stick is a lot simpler when the
EFI folder is in the .iso too. This allows just copying .iso contents
to the USB stick and EFI boot will work. While Rufus supports
extracting the boot files from efi.img, it was considered more
portable to add the copy. This also simplifies updating setup-bootable
to prepare EFI bootable disks.

- use efi.img as the image name (Rufus recognizes it)
- drop need for dosfstools, use mformat from mtools instead

Most other distros seems to do this

ref #7181

set console=hvc0 via boot option. This configuration make init to add
hvc0 to /etc/inittab and /etc/securetty. This is needed to allow login
with 'root' user.

To boot ppc64le we need to use grub with ieee1275 platform. Said that,
a new section to support grub ieee1275 was created.
Also needed to change xorrisofs command by grub-mkrescue, that is the one
used to create a bootable image for power and it is also a wrapper to xorriso.

abuild has been updated to figure this one out from $BOOTSTRAP.

- requires new abuild (from git until 2.30 is tagged)
- properly build initial musl-dev before c-compiler is available
- mark core aports with options=toolchain, and fix all makedepends
- bootstrap.sh: reorganize and use set -e there
- bootstrap.sh: use new EXTRADEPENDS_* to pull in implicit dependencies
  during bootstrap to simplify the script

we need remove the leading path to file

we need get the branch from tag instead of git branch, because we
generate releasecandidates and the first stable release from git master
and only do the git branch after the release is done.