nir: Allow nir_ssa_alu_instr_src_components to operate on non-SSA destinations

nir: Allow nir_ssa_alu_instr_src_components to operate on non-SSA destinations

Existing users only operate on instructions with SSA destinations.  Some
later patches add new direct calls and indirect calls (via existing NIR
functions) on instructions after going out of SSA.  At the very least,
these calls are added by:

intel/vec4: Try to emit a VF source in try_immediate_source
intel/vec4: Try to emit a single load for multiple 3-src instruction operands

The first commit adds direct calls, and the second adds calls via
nir_alu_srcs_equal and nir_alu_srcs_negative_equal.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>