icnss: Provide ICNSS support of reading SOC serial number

Provide support of reading SOC serial number. This will be used
for auto-generate WLAN MAC address.

CRs-Fixed: 1069005
Change-Id: Ie2072768b2fab3bcbdc70798897ca66614ee8a06
Signed-off-by: Yuanyuan Liu <yuanliu@codeaurora.org>