net: ipa: define some more IPA register fields

Define the fields for the SHARED_MEM_SIZE, QSB_MAX_WRITES,
QSB_MAX_READS, FILT_ROUT_HASH_EN, and FILT_ROUT_HASH_FLUSH IPA
registers for all supported IPA versions.

Create enumerated types to identify fields for these registers.  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>