Platform/RPi3/RpiFirmwareDxe: Add more query functions

This patch introduces the capability to also query the Model Name/
Manufacturer Name/CPU Name/Firmware Revision using the RpiFirmware
protocol. This is aims at making the driver more suitable to cater
for platforms other than the Raspberry Pi 3 as well as simplifying
the population of entries in PlatformSmbiosDxe.

Signed-off-by: Pete Batard <pete@akeo.ie>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>