In debug builds, the TSP prints its image base address and size.
The base address displayed corresponds to the start address of the
read-only section, as defined in the linker script.

This patch changes this to use the BL32_BASE address instead, which is
the same address as __RO_START__ at the moment but has the advantage
to be independent of the linker symbols defined in the linker script
as well as the layout and order of the sections.

Change-Id: I032d8d50df712c014cbbcaa84a9615796ec902cc