tools/firmware: update OVMF Makefile, when necessary

[ This is two commits from master aka staging-4.12: ]

OVMF has become dependent on OpenSSL, which is included as a
submodule.  Initialise submodules before building.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
(cherry picked from commit b16281870e)

tools: only call git when necessary in OVMF Makefile

Users may choose to export a snapshot of OVMF and build it
with xen.git supplied ovmf-makefile. In that case we don't
need to call `git submodule`.

Fixes b16281870e.

Reported-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
(cherry picked from commit 68292c94a6)

tools/firmware/ovmf-makefile

@@ -16,6 +16,7 @@ all: build
 
 .PHONY: build
 build:
+	if test -e .git ; then $(GIT) submodule update --init --recursive ; fi
 	OvmfPkg/build.sh -a X64 -b $(TARGET) -n 4
 	cp Build/OvmfX64/$(TARGET)_GCC*/FV/OVMF.fd ovmf.bin