EDAC/{skx_common,i10nm,imh}: Move MC register access helpers to skx_common

EDAC/{skx_common,i10nm,imh}: Move MC register access helpers to skx_common

Both i10nm_basic.c and imh_basic.c use identical helpers for accessing
memory controller MMIO-based registers. Move these helpers to skx_common.c
to eliminate code duplication. This change also prepares for an upcoming
patch that will move RRL(retry_rd_err_log) code from i10nm_basic.c to
skx_common.c, which requires these helpers to be available in skx_common.c.

Additionally, prefix these function names with 'skx_' to maintain naming
consistency within the file.

No functional changes intended.

Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Link: https://patch.msgid.link/20260521073112.3881223-2-qiuxu.zhuo@intel.com