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>

arch/powerpc/kernel/prom.c

@@ -712,6 +712,13 @@ void __init early_init_devtree(void *params)
 	of_scan_flat_dt(early_init_dt_scan_phyp_dump, NULL);
 #endif
 
+	/* Pre-initialize the cmd_line with the content of boot_commmand_line,
+	 * which will be empty except when the content of the variable has
+	 * been overriden by a bootloading mechanism. This happens typically
+	 * with HAL takeover
+	 */
+	strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
+
 	/* Retrieve various informations from the /chosen node of the
 	 * device-tree, including the platform type, initrd location and
 	 * size, TCE reserve, and more ...