mm: remove mmu_gathers storage from remaining architectures

Originally the mmu_gathers were removed in commit 1c39517696 ("mm: now
that all old mmu_gather code is gone, remove the storage").  However,
the openrisc and hexagon architecture were merged around the same time
and mmu_gathers was not removed.

This patch removes them from openrisc, hexagon and nds32:

Noticed while cleaning this warning:

    arch/openrisc/mm/init.c:41:1: warning: symbol 'mmu_gathers' was not declared. Should it be static?

Link: https://lkml.kernel.org/r/20220205141956.3315419-1-shorne@gmail.com
Signed-off-by: Stafford Horne <shorne@gmail.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/hexagon/mm/init.c

@@ -29,8 +29,6 @@ int max_kernel_seg = 0x303;
 /*  indicate pfn's of high memory  */
 unsigned long highstart_pfn, highend_pfn;
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 /* Default cache attribute for newly created page tables */
 unsigned long _dflt_cache_att = CACHEDEF;
 

arch/nds32/mm/init.c

@@ -18,7 +18,6 @@
 #include <asm/tlb.h>
 #include <asm/page.h>
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
 DEFINE_SPINLOCK(anon_alias_lock);
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 

arch/openrisc/mm/init.c

@@ -38,8 +38,6 @@
 
 int mem_init_done;
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 static void __init zone_sizes_init(void)
 {
 	unsigned long max_zone_pfn[MAX_NR_ZONES] = { 0 };