bug #672: pospopcount using sv.lbzu/pi/dw=8 error

bug #672: pospopcount using sv.lbzu/pi/dw=8 error

COMPLEX! this turns out to be a spec violation where RA (EA)
*must* be treated as 64-bit *NOT* have its width overridden
just because destination elwidth is set to 8-bit.
* source elwidth is supposed to apply to STORE
* dest elwidth is supposed to apply to LOAD
but those are MEMORY DATA not memory ADDRESSes they are
supposed to apply to.

TODO, most likely LDST_IDX needs fixing (RB may also need
an elwidth cancellation/override, have to check the spec)