llvmpipe: change mask input to fragment shader to 64-bit.

In order to handle a 4xMSAA mask (16-bits per sample) increase
the fragment shader API to be 64-bit.

v2: drop pointless if (Roland)

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4122>
4 files changed