i965: Move multiply by 4 for VS ATTR setup into the scalar backend.

i965: Move multiply by 4 for VS ATTR setup into the scalar backend.

The vec4 backend will want to count in units of vec4s, not scalar
components.  The simplest solution is to move the multiplication by 4
into the scalar backend.  This also improves consistency with how we
count varyings.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>