pan/bi: Stop exposing bifrost_nir_lower_load_output

Unused outside of pan/bi and also remove orphan bifrost_nir_lower_xfb
declaration.

Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: Olivia Lee <olivia.lee@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36776>

src/panfrost/compiler/bifrost_compile.c

@@ -5834,7 +5834,7 @@ bi_lower_subgroups(nir_builder *b, nir_intrinsic_instr *intr, void *data)
    return true;
 }
 
-bool
+static bool
 bifrost_nir_lower_load_output(nir_shader *nir)
 {
    assert(nir->info.stage == MESA_SHADER_FRAGMENT);

src/panfrost/compiler/bifrost_nir.h

@@ -26,6 +26,4 @@
 #include "nir_builder.h"
 
 bool bifrost_nir_lower_algebraic_late(nir_shader *shader, unsigned gpu_arch);
-bool bifrost_nir_lower_xfb(nir_shader *shader);
 bool bifrost_nir_opt_boolean_bitwise(nir_shader *shader);
-bool bifrost_nir_lower_load_output(nir_shader *nir);