ANDROID: Revert "arm64: Drop support for CMDLINE_EXTEND"

This reverts commit cae118b6ac.

Upstream removed the support for CMDLINE_EXTEND on arm64 due to some
inconsistencies in the way command-line was assembled together. However,
the patch inadvertently deleted same config option from the android tree
which was first introduced by commit 056f12819b ("ANDROID: arm64: copy
CONFIG_CMDLINE_EXTEND from ARM") back in 2014.

Upstream is currently working on a solution to fix the divergence by
allowing prepend and append functionalities. While we wait for the new
series to land let's bring back CMDLINE_EXTEND option for android, so
arm64 can actually use of the functionality provided by d9a2a3f2c2
("ANDROID: of: Support CONFIG_CMDLINE_EXTEND config option").

Bug: 120440972
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: I051f445641c8fbc3b8a13015d948f553d87cd791

arch/arm64/Kconfig

@@ -1856,6 +1856,12 @@ config CMDLINE_FROM_BOOTLOADER
 	  the boot loader doesn't provide any, the default kernel command
 	  string provided in CMDLINE will be used.
 
+config CMDLINE_EXTEND
+	bool "Extend bootloader kernel arguments"
+	help
+	  The command-line arguments provided by the boot loader will be
+	  appended to the default kernel command string.
+
 config CMDLINE_FORCE
 	bool "Always use the default kernel command string"
 	help

arch/arm64/kernel/idreg-override.c

@@ -214,8 +214,11 @@ static __init void parse_cmdline(void)
 {
 	const u8 *prop = get_bootargs_cmdline();
 
-	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !prop)
+	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) ||
+	    IS_ENABLED(CONFIG_CMDLINE_FORCE) ||
+	    !prop) {
 		__parse_cmdline(CONFIG_CMDLINE, true);
+	}
 
 	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE) && prop)
 		__parse_cmdline(prop, true);