qemu: Support SEPARATE_CODE_AND_RODATA

Update qemu_configure_mmu_##_el to add an additional region for code,
marked as MT_CODE | MT_SECURE. Update ro region attributes to NON_EXEC.

Update calls to QEMU_CONFIGURE_BLx_MMU() to pass an additional region for
code. Update calls to pass regions defined in common_def.h.

Increase MAX_MMAP_REGIONS to 10.

Enable SEPARATE_CODE_AND_RODATA by default on QEMU builds.

Fixes ARM-software/tf-issues#558

Signed-off-by: Michalis Pappas <mpappas@fastmail.fm>