i7core_edac: Convert UDIMM error counters into a proper sysfs group

Instead of displaying 3 values at the same var, break it into 3
different sysfs nodes:

/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm0
/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm1
/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm2

For registered dimms, however, the error counters are already being
displayed at:
	/sys/devices/system/edac/mc/mc0/csrow*/ce_count

So, there's no need to add any extra sysfs nodes.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>