xtensa: tlb: include <asm/tlb.h> for missing prototype

Add the prototype for check_tlb_sanity() to <asm/tlb.h> and use that
header to prevent a build warning:

arch/xtensa/mm/tlb.c:273:6: warning: no previous prototype for 'check_tlb_sanity' [-Wmissing-prototypes]
  273 | void check_tlb_sanity(void)
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Message-Id: <20230920052139.10570-13-rdunlap@infradead.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/tlb.h

@@ -18,4 +18,6 @@
 
 #define __pte_free_tlb(tlb, pte, address)	pte_free((tlb)->mm, pte)
 
+void check_tlb_sanity(void);
+
 #endif	/* _XTENSA_TLB_H */

arch/xtensa/mm/tlb.c

@@ -17,6 +17,7 @@
 #include <linux/mm.h>
 #include <asm/processor.h>
 #include <asm/mmu_context.h>
+#include <asm/tlb.h>
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>