arm: mach-omap2: Move omap5/sec-fxns.c into sec-common.c

TEE loading and firewall setup are common to all omap2 devices, move
these function out of omap5 and into mach-omap2. This allows us
to use these functions from other omap class devices.

Signed-off-by: Andrew F. Davis <afd@ti.com>