efi_loader: versioning support in GetImageInfo

Current FMP->GetImageInfo() always return 0 for the firmware
version, user can not identify which firmware version is currently
running through the EFI interface.

This commit reads the "FmpStateXXXX" EFI variable, then fills the
firmware version in FMP->GetImageInfo().

Now FMP->GetImageInfo() and ESRT have the meaningful version number.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>