net: ipa: define GSI CH_C_QOS register fields

Define the fields within the CH_C_QOS GSI register using an array of
field masks in that register's reg structure.  Use the reg functions
for encoding values in those fields.

One field in the register is present for IPA v4.0-4.2 only, two
others are present starting at IPA v4.5, and one more is there
starting at IPA v4.9.

Drop the "GSI_" prefix in symbols defined in the gsi_prefetch_mode
enumerated type, and define their values using decimal rather than
hexidecimal values.

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