arm64: mm: Export __flush_icache_range() to modules

lkdtm calls flush_icache_range(), which results in an out-of-line call
to __flush_icache_range(), which is not exported to modules.

Export the symbol to modules to fix this build breakage.

Fixes: 3b8c9f1cdf ("arm64: IPI each CPU after invalidating the I-cache for kernel mappings")
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/flush.c

@@ -82,7 +82,7 @@ EXPORT_SYMBOL(flush_dcache_page);
 /*
  * Additional functions defined in assembly.
  */
-EXPORT_SYMBOL(flush_icache_range);
+EXPORT_SYMBOL(__flush_icache_range);
 
 #ifdef CONFIG_ARCH_HAS_PMEM_API
 void arch_wb_cache_pmem(void *addr, size_t size)