net: ipa: a few last IPA register cleanups

Some last cleanups for the existing IPA register definitions:
  - Remove the definition of IPA_REG_ENABLED_PIPES_OFFSET, because
    it is not used.
  - Use "IPA_" instead of "BAM_" as the prefix on fields associated
    with the FLAVOR_0 register.  We use GSI (not BAM), but the
    fields apply to both GSI and BAM.
  - Get rid of the definition of IPA_CS_RSVD; it is never used.
  - Add two missing field mask definitions for the INIT_DEAGGR
    endpoint register.
  - Eliminate a few of the defined sequencer types, because they
    are unused.  We can add them back when needed.
  - Add a field mask to indicate which bit causes an interrupt on
    the microcontroller.

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