net: ipa: define CLKON_CFG and ROUTE IPA register fields

Create the ipa_reg_clkon_cfg_field_id enumerated type, which
identifies the fields for the CLKON_CFG IPA register.  Add "CLKON_"
to a few short names to try to avoid name conflicts.  Create the
ipa_reg_route_field_id enumerated type, which identifies the fields
for the ROUTE IPA register.

Use IPA_REG_FIELDS() to specify the field mask values defined for
these registers, for each supported version of IPA.

Use ipa_reg_bit() and ipa_reg_encode() to build up the values to be
written to these registers rather than using the *_FMASK
preprocessor symbols.

Remove the definition of the now unused *_FMASK symbols.

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