rockchip: capsule: Add functions for supporting capsule updates

Add functions needed to support the UEFI capsule update feature on
rockchip boards. Currently, the feature is being enabled on the
RockPi4 boards with firmware images residing on GPT partitioned
storage media.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>