svga: fix git_sha1.h include path in Android.mk (v3)

svga: fix git_sha1.h include path in Android.mk (v3)

Adds libmesa_git_sha1 static (dummy) library to generate git_sha1.h
with some polishing to header dependency on .git/HEAD and scripted rules.

The now redundant generation rules are removed from Android.gen.mk
libmesa_git_sha1 whole static depedency is added to libmesa_pipe_svga,
libmesa_dricore and libmesa_st_mesa modules

Fixes the following building error:

external/mesa/src/gallium/drivers/svga/svga_screen.c:26:10:
fatal error: 'git_sha1.h' file not found
         ^
1 error generated.

Fixes: 1ce3a27 ("svga: Add the ability to log messages to
vmware.log on the host.")
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>