bcma: add support for on-chip OTP memory used for SPROM storage

Wireless Broadcom chips can have either their SPROM data stored
on either external SPROM or on-chip OTP memory. Both are accessed
through the same register space. This patch adds support for the
on-chip OTP memory.

Tested with:
BCM43224 OTP and SPROM
BCM4331 SPROM
BCM4313 OTP

This patch is in response to linux-wireless thread [1].

[1] http://article.gmane.org/gmane.linux.kernel.wireless.general/85426



Tested-by: Saul St. John <saul.stjohn@gmail.com>
Tested-by: Rafal Milecki <zajec5@gmail.com>
Tested-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>