BL2 is responsible for loading BL32 and passing a pointer to the
BL32 entrypoint info to BL31 in the BL31 parameters. If no BL32
image is loaded, a NULL pointer is passed. The platform is
responsible for accessing BL31 parameters and extracting the
corresponding BL32 EP info.

In ARM platforms, arm_bl31_early_platform_setup() dereferences the
pointer to the BL32 EP info without checking first if the pointer
is NULL. This will cause an exception if a BL32 entrypoint has not
been populated by BL2. FVP and Juno are not affected because they
always define BL32_BASE, irrespective of whether a BL32 image is
included in the FIP or not.

This patches fixes the issue by checking the BL32 ep_info pointer
before trying to access the data.

If `RESET_TO_BL31` is enabled, the BL32 entrypoint is not
populated if BL32_BASE is not defined.

NOTE: Maintainers of partner platforms should check for this issue
in their ports.

Fixes ARM-software/tf-issues#320

Change-Id: I31456155503f2765766e8b7cd30ab4a40958fb96