If PLAT_RO_XLAT_TABLES is defined, the base xlat table goes to the
.rodata section instead of .bss section.

This causes a warning like:

/tmp/ccswitLr.s: Assembler messages:
/tmp/ccswitLr.s:297: Warning: setting incorrect section attributes for .rodata

It is practically no problem, but I want to keep the build log clean.

Put the base table into the "base_xlat_table" section to suppress the
assembler warnings.

The linker script determines its final destination; rodata section if
PLAT_RO_XLAT_TABLES=1, or bss section otherwise. So, the result is the
same.

Change-Id: Ic85d1d2dddd9b5339289fc2378cbcb21dd7db02e
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>