net: ipa: fix BCR register field definitions

The backward compatibility register field masks are defined using
single-bit masks defined with BIT(x) rather than GENMASK(x, x).
Change this one set of definitions to follow the GENMASK() pattern
used everywhere else.  Add a few missing field definitions for this
register as well.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>