SPM: Move S-EL1/S-EL0 xlat tables to TZC DRAM

A new platform define, `PLAT_SP_IMAGE_XLAT_SECTION_NAME`, has been
introduced to select the section where the translation tables used by
the S-EL1/S-EL0 are placed.

This define has been used to move the translation tables to DRAM secured
by TrustZone.

Most of the extra needed space in BL31 when SPM is enabled is due to the
large size of the translation tables. By moving them to this memory
region we can save 44 KiB.

A new argument has been added to REGISTER_XLAT_CONTEXT2() to specify the
region where the translation tables have to be placed by the linker.

Change-Id: Ia81709b4227cb8c92601f0caf258f624c0467719
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>