firmware: Improve comments for fw_prev_arg1() and fw_next_arg1()

The state of a0, a1, and a2 registers in fw_prev_arg1() and
fw_next_arg1() is same as passed by previous booting stage
so we add this info in comments for both these functions.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

firmware/fw_dynamic.S

@@ -91,6 +91,8 @@ fw_save_info:
 	.global fw_prev_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The previous arg1 should be returned in 'a0'.
 	 */
 fw_prev_arg1:
@@ -102,6 +104,8 @@ fw_prev_arg1:
 	.global fw_next_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The next arg1 should be returned in 'a0'.
 	 */
 fw_next_arg1:

firmware/fw_jump.S

@@ -39,6 +39,8 @@ fw_save_info:
 	.global fw_prev_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The previous arg1 should be returned in 'a0'.
 	 */
 fw_prev_arg1:
@@ -50,6 +52,8 @@ fw_prev_arg1:
 	.global fw_next_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The next arg1 should be returned in 'a0'.
 	 */
 fw_next_arg1:

firmware/fw_payload.S

@@ -39,6 +39,8 @@ fw_save_info:
 	.global fw_prev_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The previous arg1 should be returned in 'a0'.
 	 */
 fw_prev_arg1:
@@ -54,6 +56,8 @@ fw_prev_arg1:
 	.global fw_next_arg1
 	/*
 	 * We can only use a0, a1, and a2 registers here.
+	 * The a0, a1, and a2 registers will be same as passed by
+	 * previous booting stage.
 	 * The next arg1 should be returned in 'a0'.
 	 */
 fw_next_arg1: