util/update_release_branch: Add support for internal branches
util/update_release_branch: Add support for internal branches

This adds support for updating internal (private) branches. These are
distinguished by using the "cros-internal" branch name prefix instead of
the usual "cros" prefix. This is done by adding a "--remote_prefix"
option to override the default "cros" prefix".

In addition, since the notion of "baseboard" or "board" does not exist
in some repos, the use of these flags is no longer mandated. The
"--relevant_path_file" can still be used to augment the generated commit
message in these cases.

Plus, minor lint improvements suggested by repo upload.

BRANCH=none
BUG=b:244387210
TEST=performed update on a private branch. ran:
	".../util/update_release_branch.py --remote_prefix cros-internal
	<internal-branch-name>" and confirmed branch files were updated
	to match ToT.

Change-Id: I97e48cfe068ba5a1b7774c256262accf75ce763a
Signed-off-by: Caveh Jalali <08e24a66aefda7a55ca7d73f8903e0fb16eec763@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3885227
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec