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>