net: ipa: update GSI ring size registers

Each GSI channel has a CNTXT_1 register that encodes the size of its
ring buffer.  The size of the field that records that is increased
starting at IPA v4.9.  Replace the use of a fixed-size field mask
with a new inline function that encodes that size value.

Similarly, the size of GSI event rings can be larger starting with
IPA v4.9, so create a function to encode that as well.

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