broadcom/compiler: always enable per-quad on spill operations

broadcom/compiler: always enable per-quad on spill operations

This ensures that any channels used for helper invocations are
also spilled/filled correctly.

Alternatively, we could recursively track all temps that get
involved in computing values that are then used in explicit
(dfdx,dfdy) or implicit (texture coordinates for mipmap or
anisotropic filtering, etc) derivatives, and only enable
per-quad on these (or disable spilling of any of these
values).

Fixes:
dEQP-VK.graphicsfuzz.cov-dfdx-dfdy-after-nested-loops

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15705>