LoongArch: Use correct API to map cmdline in relocate_kernel()

fw_arg1 is in memory space rather than I/O space, so we should use
early_memremap_ro() instead of early_ioremap() to map the cmdline.
Moreover, we should unmap it after using.
Suggested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kernel/relocate.c

@@ -13,6 +13,7 @@
 #include <asm/bootinfo.h>
 #include <asm/early_ioremap.h>
 #include <asm/inst.h>
+#include <asm/io.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
 
@@ -196,7 +197,7 @@ unsigned long __init relocate_kernel(void)
 	unsigned long kernel_length;
 	unsigned long random_offset = 0;
 	void *location_new = _text; /* Default to original kernel start */
-	char *cmdline = early_ioremap(fw_arg1, COMMAND_LINE_SIZE); /* Boot command line is passed in fw_arg1 */
+	char *cmdline = early_memremap_ro(fw_arg1, COMMAND_LINE_SIZE); /* Boot command line is passed in fw_arg1 */
 
 	strscpy(boot_command_line, cmdline, COMMAND_LINE_SIZE);
 
@@ -208,6 +209,7 @@ unsigned long __init relocate_kernel(void)
 		random_offset = (unsigned long)location_new - (unsigned long)(_text);
 #endif
 	reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
+	early_memunmap(cmdline, COMMAND_LINE_SIZE);
 
 	if (random_offset) {
 		kernel_length = (long)(_end) - (long)(_text);