compiler/nir: add lowering for 16-bit flrp

And enable it on Intel.

v2:
 - Squash the change to enable it on Intel (Jason)

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

src/compiler/nir/nir.h

@@ -2163,6 +2163,7 @@ typedef struct nir_shader_compiler_options {
    bool lower_fdiv;
    bool lower_ffma;
    bool fuse_ffma;
+   bool lower_flrp16;
    bool lower_flrp32;
    /** Lowers flrp when it does not support doubles */
    bool lower_flrp64;