feat(plat/st): implement platform functions for SMCCC_ARCH_SOC_ID

The JEDEC information for STMicroelectronics is:
JEDEC_ST_MFID U(0x20)
JEDEC_ST_BKID U(0x0)
And rely on platform functions to get chip IP and revision.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I4fa4ac8bb5583b1871b768decc9fe08e8966ff54
2 files changed