bcma: mark nflash if it is the boot flash

There are some devices which are able to boot from nand flash and other
are using a serial flash for booting. Add a bool to indicate that the
device is booted from that flash chip and not from some other chip also
connected to the SoC. This is needed to find the nvram, as it is stored
on the flash the devices booted from.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>