net: ipa: GSI register cleanup

Move some static inline function definitions out of "gsi_reg.h" and
into "gsi.c", which is the only place they're used.  Rename them so
their names identify the register they're associated with.

Move the gsi_channel_type enumerated type definition below the
offset and field definitions for the CH_C_CNTXT_0 register where
it's used.

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