Makefile: install the edk2 firmware images and their descriptors

Makefile: install the edk2 firmware images and their descriptors

Decompress and install the edk2 firmware blobs as part of "make install",
unless blob installation was disabled with configure's "--disable-blobs"
option.

Additionally, decompress the blobs as a pre-requisite for building softmmu
binaries -- this is helpful for both "make check" and other ad-hoc tests
one might want to run in the build directory.

Signed-off-by: Laszlo Ersek <[email protected]>
Reviewed-by: Michal Privoznik <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Igor Mammedov <[email protected]>