i7core_edac: Properly mark const static vars as such

There are two groups of sysfs attributes: one for rdimm and another
for udimm. Instead of changing dynamically the unique static struct
for handling udimm's, declare two vars and make them constant.

This avoids the risk of having two or more memory controllers, each
needing a different set of attributes.

While here, use const on all places where it is applicable.

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

edac_core: use const for constant sysfs arguments

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