Fold is_ram_rom and is_ram_rom_romd() into callers.

Change is_romd() and section_addr() to take MemoryRegion
instead of MemoryRegionSection for consistency and
use memory_region_ prefix.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>