When building OpenSBI via a submodule, OPENSBI_VERSION_GIT can be left
unset in case '.git' isn't a dir. This is the case when building OpenSBI
as a QEMU submodule:
$ cat .git
gitdir: ../../.git/modules/roms/opensbi
As a result, building OpenSBI tag v1.5.1 in QEMU will result in a binary
that will have "OpenSBI v1.5" as a banner.
Use "git rev-parse --git-dir" instead of checking if '.git' is a dir to
detect if the current dir is a git repo.
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
