i965/fs: shuffle_32bit_load_result_to_16bit_data now skips components

i965/fs: shuffle_32bit_load_result_to_16bit_data now skips components

This helper used to load 16bit components from 32-bits read now allows
skipping components with the new parameter first_component. The semantics
now skip components until we reach the first_component, and then reads the
number of components passed to the function.

All previous uses of the helper are updated to use 0 as first_component.
This will allow read 16-bit components when the first one is not aligned
32-bit. Enabling more usages of untyped_reads with 16-bit types.

v2: (Jason Ektrand)
    Change parameters order to first_component, num_components

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>