IntelSiliconPkg/BootMediaLib: Reduce library API

Removes the following functions from FirmwareBootMediaLib.h:
 * FirmwareBootMediaIsSpi ()
 * FirmwareBootMediaIsUfs ()
 * FirmwareBootMediaIsEmmc ()
 * FirmwareBootMediaIsNvme ()

It is preferred to have a single method to retrieve the firmware
boot media. To reduce overall maintenance effort over time, the
FirmwareBootMediaIsXxx () pattern is removed in favor of returning
the firmware boot media type via GetFirmwareBootMediaType ().

Cc: Sai Chaganty <rangasai.v.chaganty@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Michael Kubacki <michael.a.kubacki@intel.com>
Reviewed-by: Sai Chaganty <rangasai.v.chaganty@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>