Add kernel 5.15 for RPI4 support

root/target/linux/bcm27xx/patches-5.15/0048-spi-spidev-Completely-disable-the-spidev-warning.patch

@@ -0,0 +1,29 @@
+From 0322d4639d99a2c0e472aee8996b566699b6355d Mon Sep 17 00:00:00 2001
+From: Phil Elwell <phil@raspberrypi.org>
+Date: Tue, 14 Jul 2015 10:26:09 +0100
+Subject: [PATCH 048/634] spi: spidev: Completely disable the spidev warning
+
+An alternative strategy would be to use "rpi,spidev" instead, but that
+would require many Raspberry Pi Device Tree changes.
+
+Signed-off-by: Phil Elwell <phil@raspberrypi.org>
+---
+ drivers/spi/spidev.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
+index 795bef1efcc6..9a3b8a51eaef 100644
+--- a/drivers/spi/spidev.c
++++ b/drivers/spi/spidev.c
+@@ -746,7 +746,7 @@ static int spidev_probe(struct spi_device *spi)
+ 	 * compatible string, it is a Linux implementation thing
+ 	 * rather than a description of the hardware.
+ 	 */
+-	WARN(spi->dev.of_node &&
++	WARN(0 && spi->dev.of_node &&
+ 	     of_device_is_compatible(spi->dev.of_node, "spidev"),
+ 	     "%pOF: buggy DT: spidev listed directly in DT\n", spi->dev.of_node);
+ 
+-- 
+2.33.1
+