i965/fs: Remove the width field from fs_reg

i965/fs: Remove the width field from fs_reg

As of now, the width field is no longer used for anything.  The width field
"seemed like a good idea at the time" but is actually entirely redundant
with the instruction's execution size.  Initially, it gave us the ability
to easily set the instructions execution size based entirely on register
widths.  With the builder, we can easiliy set the sizes explicitly and the
width field doesn't have as much purpose.  At this point, it's just
redundant information that can get out of sync so it really needs to go.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Acked-by: Francisco Jerez <currojerez@riseup.net>