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: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>