soc/amd/*/data_fabric: introduce and use DF_MMIO_REG_SET_SIZE

soc/amd/*/data_fabric: introduce and use DF_MMIO_REG_SET_SIZE

To be able to handle a special case, add a per-SoC define for
DF_MMIO_REG_SET_SIZE instead of having this hard-coded as 4 in the
DF_MMIO_* macros. To avoid some duplication, also introduce the
DF_MMIO_REG_OFFSET macro.

TEST=Output from data_fabric_print_mmio_conf doesn't change on Mandolin.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I67420a2973c8ef9a7f0ce19ddc0013de69731689
Reviewed-on: https://review.coreboot.org/c/coreboot/+/72878
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>