radv: Allow interpolation on non-float types.

In particular structs containing floats and 16-bit floating point
types.

Fixes: 62024fa7 "radv: enable VK_KHR_16bit_storage extension / 16bit storage features"
Fixes: da295946 "spirv: Only split blocks"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109735


Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit f3247841)