MIPS: Remove struct mm_context_t fp_mode_switching field

The fp_mode_switching field in struct mm_context_t was left unused by
commit 8c8d953c28 ("MIPS: Schedule on CPUs we need to lose FPU for a
mode switch") in v4.19, with nothing modifying its value & nothing
waiting on it having any particular value after that commit. Remove the
unused field & the one remaining reference to it.

Signed-off-by: Paul Burton <paul.burton@mips.com>

arch/mips/include/asm/mmu.h

@@ -9,7 +9,6 @@
 typedef struct {
 	u64 asid[NR_CPUS];
 	void *vdso;
-	atomic_t fp_mode_switching;
 
 	/* lock to be held whilst modifying fp_bd_emupage_allocmap */
 	spinlock_t bd_emupage_lock;