ANDROID: scripts/setlocalversion: allow running in a subdir

Getting the scmversion using scripts/setlocalversion currently only
works when run at the root of a git or mecurial project. This was
introduced in commit 8558f59e ("setlocalversion: Ignote SCMs above
the linux source tree") so that if one is building within a subdir of
a git tree that isn't the kernel git project, then the vermagic wouldn't
include that git sha1.

For Android purposes, this isn't a concern. So let's bring back this
functionality so that we can use scripts/setlocalversion to capture the SCM
version of external modules that reside within subdirectories of an SCM
project.

Bug: 180027765
Link: https://lore.kernel.org/lkml/20201125010541.309848-2-willmcvicker@google.com


Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: If12ea75c6be0c0167f29f69b7cf13d1d85b7331c