android: r600/sfn: add sfn_nir_lower_64bit.cpp to Makefile.sources

Fixes the following building errors:

FAILED: out/target/product/x86_64/obj/SHARED_LIBRARIES/gallium_dri_intermediates/LINKED/gallium_dri.so ... ld.lld: error: undefined symbol: r600::r600_nir_split_64bit_io(nir_shader*)

referenced by sfn_nir.cpp:981 (external/mesa/src/gallium/drivers/r600/sfn/sfn_nir.cpp:981) ... ld.lld: error: undefined symbol: r600::r600_nir_64_to_vec2(nir_shader*) referenced by sfn_nir.cpp:1010 (external/mesa/src/gallium/drivers/r600/sfn/sfn_nir.cpp:1010) ... ld.lld: error: undefined symbol: r600::r600_merge_vec2_stores(nir_shader*) referenced by sfn_nir.cpp:1015 (external/mesa/src/gallium/drivers/r600/sfn/sfn_nir.cpp:1015)

Fixes: 165fb511 ("r600/sfn: add lowering passes to get 64 bit ops lowered to 32 bit vec2") Cc: 21.0 Signed-off-by: Mauro Rossi issor.oruam@gmail.com