EDAC/ie31200: Make struct dimm_data contain decoded information

The current dimm_data structure contains encoded DIMM information,
which needs to be decoded for a given SoC when it is used. Make it
contain decoded information when it's initialized so that the places
where it is used do not need to decode it again, thereby simplifying
the code.

No functional changes intended.

Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Tested-by: Gary Wang <gary.c.wang@intel.com>
Link: https://lore.kernel.org/r/20250310011411.31685-8-qiuxu.zhuo@intel.com