net: ipa: add more GSI register definitions

Continue populating with GSI register definitions, adding remaining
registers whose offset depends on a channel ID.  Use gsi_reg() and
reg_n_offset() to determine offsets for those registers, and get rid
of the corresponding GSI_CH_C_*_OFFSET() macros.

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