tools/firmware/hvmloader: rework Makefile

tools/firmware/hvmloader: rework Makefile

Setup proper dependencies with libacpi so we don't need to run "make
hvmloader" in the "all" target. ("build.o" new prerequisite isn't
exactly proper but a side effect of building the $(DSDT_FILES) is to
generate the "ssdt_*.h" needed by "build.o".)

Make use if "-iquote" instead of a plain "-I".

For "roms.inc" target, use "$(SHELL)" instead of plain "sh". And use
full path to "mkhex" instead of a relative one. Lastly, add "-f" flag
to "mv" to avoid a prompt in case the target already exist and we
don't have write permission.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>