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In order to configure and boot SCP, BL31 has to compute and send
the SHA-256 of the firmware data via scpi. Luckily Amlogic GXL SOC
has a DMA facility that could be used to offload SHA-256
computations. This adds basic support of this hardware SHA-256
engine.
Signed-off-by: Remi Pommarel <repk@triplefau.lt>