AXI_LIMIT_*_M1 naming

Submitting this as a GitLab exercise as much as anything.

Defines like "AXI_LIMIT_SRAM_MAX_OUTSTANDING_READ_M1" don't make sense - the "M1" in the hardware field name denotes "minus 1". But the value of the define is the actual limit, from which the driver subtracts 1 itself before programming.

Hence the M1 should not be included in the define name. As it isn't for U55/U65.

You could justify adding the "_M1" to match the hardware field, but in that case the driver should not be subtracting 1 from it and setting that field directly.

Which is what MAX_BEATS is doing - although then it suffers from the hardware naming not being ideal - it is a byte-based value as the U55/U65 naming tried to indicate. Would be clearer if the enum MAX_BEATS_B256 could be used matching the hardware manual rather than raw numbers.