Replace branch_pmos and branch_alpine keys (that were never used) with a
new channel key. pmbootstrap will look up the branches related to a
channel in channels.cfg of the master branch. While at it, modernize the
file.
[skip-ci]: just downloading all kernel sources takes about one hour
and ollieparanoid wants to merge it now. This already ran
successfully with [ci:skip-build] and [ci:skip-vercheck].
Prepare for better device categorization by moving everything to testing
subdir first.
[skip-ci]: chicken-egg problem: passing pmaports CI depends on pmbootstrap MR
depends on this MR
Related: postmarketos#16
Require the pmbootstrap version where building kernels for armhf is
fixed (triplet change is involved), and where the abuild-tar-workaround
for aarch64 is not used anymore (so we can remove the package in
pmaports).
Require latest pmbootstrap version, because it supports depends in
depends in the APKBUILD parser, and is able to properly test
UEVENT_HELPER, LBDAP kconfig options (they must depend on the kernel
version).
This version has the "crossdirect" package, which will be required for
the new pmbootstrap code that uses the crossdirect compilation method by
default.
