amd64_edac: beef up DRAM error injection

When injecting DRAM ECC errors (F3xBC_x8), EccVector[15:0] is a bitmask
of which bits should be error injected when written to and holds the
payload of 16-bit DRAM word when read, respectively.

Add /sysfs members to show the DRAM ECC section/word/vector.

Fail wrong injection values entered over /sysfs instead of truncating
them.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>