Implement the first part of the BB read workaround.

Implement the first part of the BB read workaround.

The AR5008/AR9001 series NICs have a bug where BB register reads
will occasionally be corrupted. This could cause issues with things
such as ANI, which adjust operational parameters based on the
BB radio register reads. This was introduced in the AR5008 chip
and fixed with the first released AR9002 series NIC (AR9280v2.)

A followup commit will implement the acutal WAR when reading
BB registers. I'm still not sure how I'll implement it - whether
it should be done in the osdep layer, or whether it should just
live in the AR5416 HAL. Either way, they can use this capability
bit to determine whether to implement the WAR or not.

Thankyou to various sources inside Atheros who have helped me track
down what this particular issue is.

Obtained from:	Atheros