net: ipa: update IPA aggregation registers for IPA v4.5

IPA v4.5 significantly changes the format of the configuration
register used for endpoint aggregation.  The AGGR_BYTE_LIMIT field
is now larger, and the positions of other fields are shifted.  This
complicates the way we have to access this register because functions
like u32_encode_bits() require their field mask argument to be constant.

A further complication is that we want to know the maximum value
representable by at least one of these fields, and that too requires
a constant field mask.

This patch adds support for IPA v4.5 endpoint aggregation registers
in a way that continues to support "legacy" IPA hardware.  It does
so in a way that keeps field masks constant.

First, for each variable field mask, we define an inline function
whose return value is either the legacy value or the IPA v4.5 value.

Second, we define functions for these fields that encode a value
to use in each field based on the IPA version (this approach is
already used elsewhere).  The field mask provided is supplied by
the function mentioned above.

Finally, for the aggregation byte limit fields where we want to
know the maximum representable value, we define a function that
returns that maximum, computed from the appropriate field mask.

We can no longer verify at build time that our buffer size is
in the range that can be represented by the aggregation byte
limit field.  So remove the test done by a BUILD_BUG_ON() call
in ipa_endpoint_validate_build(), and implement a comparable check
at the top of ipa_endpoint_data_valid().

Doing that makes ipa_endpoint_validate_build() contain a single
line BUILD_BUG_ON() call, so just remove that function and move
the remaining line into ipa_endpoint_data_valid().

One final note:  the aggregation time limit value for IPA v4.5 needs
to be computed differently.  That is handled in an upcoming patch.

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

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