net: ipa: share field mask values for GSI general interrupt

The GSI general interrupt is managed by three registers: enable;
status; and clear.  The three registers have same set of field bits
at the same locations.  Use a common set of field masks for all
three registers to avoid duplication.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>