net: ipa: define fields for remaining GSI registers

Define field IDs for the remaining GSI registers, and populate the
register definition files accordingly.  Use the reg_*() functions to
access field values for those regiters, and get rid of the previous
field definition constants.

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