mkeficapsule: Remove raw and FIT GUID types

While building a capsule, the GUID value of that specific image is to
be passed through the --guid command option to the mkeficapsule
tool instead of using one of --raw or --fit options, where the GUID
value passed through the command line option is the image GUID.

This renders the EFI_FIRMWARE_IMAGE_TYPE_UBOOT_FIT_GUID and
EFI_FIRMWARE_IMAGE_TYPE_UBOOT_RAW_GUID values superfluous. Remove the
--raw and --fit command line options as well. Also modify the
mkeficapsule man page to reflect this change.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>