sparc: cacheflush_32.h needs struct page

Add a struct page forward declaration to cacheflush_32.h.
Fixes this build warning:

    CC      drivers/crypto/xilinx/zynqmp-sha.o
  In file included from arch/sparc/include/asm/cacheflush.h:11,
                   from include/linux/cacheflush.h:5,
                   from drivers/crypto/xilinx/zynqmp-sha.c:6:
  arch/sparc/include/asm/cacheflush_32.h:38:37: warning: 'struct page' declared inside parameter list will not be visible outside of this definition or declaration
     38 | void sparc_flush_page_to_ram(struct page *page);

Exposed by commit 0e03b8fd ("crypto: xilinx - Turn SHA into a
tristate and allow COMPILE_TEST") but not Fixes: that commit because the
underlying problem is older.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David S. Miller <davem@davemloft.net>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: sparclinux@vger.kernel.org
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sparc/include/asm/cacheflush_32.h

@@ -35,6 +35,7 @@
 #define flush_page_for_dma(addr) \
 	sparc32_cachetlb_ops->page_for_dma(addr)
 
+struct page;
 void sparc_flush_page_to_ram(struct page *page);
 
 #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1