refactor(plat/st): export functions to get SoC information

Three functions are exported to get SoC version, SoC device ID, and SoC
name. Those functions are based on reworked existing static functions.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I1f3949062bb488286a9e7a38ffcd1457953dac56
3 files changed