Add kernel 5.15 for RPI4 support

root/target/linux/bcm27xx/patches-5.15/0205-drivers-char-vcio-Use-common-compat-header.patch

@@ -0,0 +1,28 @@
+From a6d27048e25d448455ccbbdd5bd98cdd6e8d4375 Mon Sep 17 00:00:00 2001
+From: Phil Elwell <phil@raspberrypi.com>
+Date: Mon, 2 Mar 2020 14:40:19 +0000
+Subject: [PATCH 205/634] drivers: char: vcio: Use common compat header
+
+The definition of compat_ptr is now common for most platforms, but
+requires the inclusion of <linux/compat.h>.
+
+Signed-off-by: Phil Elwell <phil@raspberrypi.com>
+---
+ drivers/char/broadcom/vcio.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/drivers/char/broadcom/vcio.c b/drivers/char/broadcom/vcio.c
+index d2598663a2b5..a39155a94fb7 100644
+--- a/drivers/char/broadcom/vcio.c
++++ b/drivers/char/broadcom/vcio.c
+@@ -18,6 +18,7 @@
+ #include <linux/module.h>
+ #include <linux/slab.h>
+ #include <linux/uaccess.h>
++#include <linux/compat.h>
+ #include <soc/bcm2835/raspberrypi-firmware.h>
+ 
+ #define MBOX_CHAN_PROPERTY 8
+-- 
+2.33.1
+