RISC-V: move empty_zero_page definition to C and export it

Needed by some modules (exported by other architectures).
Signed-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/head.S

@@ -152,6 +152,3 @@ END(_start)
 __PAGE_ALIGNED_BSS
 	/* Empty zero page */
 	.balign PAGE_SIZE
-ENTRY(empty_zero_page)
-	.fill (empty_zero_page + PAGE_SIZE) - ., 1, 0x00
-END(empty_zero_page)

arch/riscv/kernel/setup.c

@@ -60,6 +60,9 @@ static char __initdata builtin_cmdline[COMMAND_LINE_SIZE] = CONFIG_CMDLINE;
 unsigned long va_pa_offset;
 unsigned long pfn_base;
 
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
+EXPORT_SYMBOL(empty_zero_page);
+
 /* The lucky hart to first increment this variable will boot the other cores */
 atomic_t hart_lottery;