board/ti/am335x: add support for beaglebone NOR Cape

This patch adds support of NOR cape[1] for both Beaglebone (white) and
Beaglebone(Black) boards. NOR Flash on this cape is connected to GPMC
chip-select[0] and accesses as external memory-mapped device.
This cape has 128Mbits(16MBytes), x16, CFI compatible NOR Flash device.

As GPMC chip-select[0] can be shared by multiple capes so NOR profile is
not enabled by default in boards.cfg. Following changes are required to
enable NOR cape detection when building am335x_boneblack board profile.

Signed-off-by: Tom Rini <trini@ti.com>