ARM: 6997/1: ep93xx: increase NR_BANKS to 16 for support of 128MB RAM

I've got hands on one ts-7300 board, which is equiped with 128MB RAM in two
64MB memory chips, so it's 16 banks/8MB each. Without this patch, the bootmem
init code complains about small NR_BANKS number and only lower 64MB is
accessible.

Cc: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>