EFI: FMP: Use a common GetImageInfo function for FIT and raw images

The GetImageInfo function definitions for the FIT images and raw
images are the same. Use a common function for the both the Firmware
Management Protocol(FMP) instances for raw and FIT images.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>