riscv: mm: Drop redundant _sdata and _edata declaration

The _sdata/_edata is already in sections.h, drop redundant
declaration.

Also move _xiprom/_exiprom declarations at the beginning of
the file, cleanup one CONFIG_XIP_KERNEL.
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/mm/init.c

@@ -33,6 +33,7 @@ unsigned long kernel_virt_addr = KERNEL_LINK_ADDR;
 EXPORT_SYMBOL(kernel_virt_addr);
 #ifdef CONFIG_XIP_KERNEL
 #define kernel_virt_addr       (*((unsigned long *)XIP_FIXUP(&kernel_virt_addr)))
+extern char _xiprom[], _exiprom[];
 #endif
 
 unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
@@ -171,13 +172,6 @@ static void __init setup_bootmem(void)
 	memblock_allow_resize();
 }
 
-#ifdef CONFIG_XIP_KERNEL
-
-extern char _xiprom[], _exiprom[];
-extern char _sdata[], _edata[];
-
-#endif /* CONFIG_XIP_KERNEL */
-
 #ifdef CONFIG_MMU
 static struct pt_alloc_ops _pt_ops __ro_after_init;