powerpc/powernv: Get kernel command line accross OPAL takeover

We stash it in boot_command_line which isn't in BSS and so won't
be overwritten. We then use that as a default cmd_line before
we walk the device-tree.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index 9369287..e3f3904 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -1449,6 +1449,10 @@
 		opal_addr = top_addr;
 	args->hal_addr = opal_addr;
 
+	/* Copy the command line to the kernel image */
+	strlcpy(RELOC(boot_command_line), RELOC(prom_cmd_line),
+		COMMAND_LINE_SIZE);
+
 	prom_debug("  k_image    = 0x%lx\n", args->k_image);
 	prom_debug("  k_size     = 0x%lx\n", args->k_size);
 	prom_debug("  k_entry    = 0x%lx\n", args->k_entry);