nir: Add multiplier argument to nir_lower_uniforms_to_ubo.

nir: Add multiplier argument to nir_lower_uniforms_to_ubo.

Note that locations can be set in different units, and the multiplier
argument caters to supporting these different units. For example,
st_glsl_to_nir uses dwords (4 bytes) so the multiplier should be 4,
while tgsi_to_nir uses bytes, so the multiplier should be 16.

Signed-Off-By: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Andre Heider <a.heider@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Eric Anholt <eric@anholt.net>