Update Linux to v5.4.148

Sourced from [1]

[1] https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.4.148.tar.gz

Change-Id: Ib3d26c5ba9b022e2e03533005c4fed4d7c30b61b
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/include/linux/tty.h b/include/linux/tty.h
index bfa4e2e..eb33d94 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -66,7 +66,7 @@
 	int read;
 	int flags;
 	/* Data points here */
-	unsigned long data[0];
+	unsigned long data[];
 };
 
 /* Values for .flags field of tty_buffer */
@@ -225,6 +225,8 @@
 	void (*write_wakeup)(struct tty_port *port);
 };
 
+extern const struct tty_port_client_operations tty_port_default_client_ops;
+
 struct tty_port {
 	struct tty_bufhead	buf;		/* Locked internally */
 	struct tty_struct	*tty;		/* Back pointer */
@@ -304,6 +306,10 @@
 	struct termiox *termiox;	/* May be NULL for unsupported */
 	char name[64];
 	struct pid *pgrp;		/* Protected by ctrl lock */
+	/*
+	 * Writes protected by both ctrl lock and legacy mutex, readers must use
+	 * at least one of them.
+	 */
 	struct pid *session;
 	unsigned long flags;
 	int count;