Add SRC_GITREVCOUNT to calculate the relevant git commits of
"src_path" or "src_files" to package's revision.
Test Plan:
Pass: build-pkgs -c -p systemd-presets,shim
Pass: Observe relevant git commits of 'src_path' or 'src_files'
are added to package's revision
Story: 2010550
Task: 47537
Depends-On: https://review.opendev.org/c/starlingx/root/+/875584
Signed-off-by: Yue Tao <yue.tao@windriver.com>
Change-Id: I9852f534c53664e89e8b0082d2e68b3d9333d6f9
2a3b5c8349