configs/raspberrypi2: update and fix our defconfig

Lock to 3.19 kernel headers; and comment about installing DTBs; bump
kernel sha1.

Reported-by: Peter Korsgaard <jacmet@uclibc.org>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/raspberrypi2_defconfig

@@ -2,14 +2,24 @@ BR2_arm=y
 BR2_cortex_a7=y
 BR2_ARM_EABIHF=y
 BR2_ARM_FPU_NEON_VFPV4=y
+
 BR2_TOOLCHAIN_BUILDROOT_LARGEFILE=y
 BR2_TOOLCHAIN_BUILDROOT_CXX=y
+
 BR2_TARGET_GENERIC_GETTY_PORT="tty1"
+
+# Lock to 3.19 headers as the RPi2 kernel is based off the 3.19 branch
+BR2_KERNEL_HEADERS_VERSION=y
+BR2_DEFAULT_KERNEL_VERSION="3.19"
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_19=y
+
 BR2_LINUX_KERNEL=y
 BR2_LINUX_KERNEL_CUSTOM_GIT=y
 BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/raspberrypi/linux.git"
-BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="3c9fd364bfa6c0f6ef725d74b72a9b77dd0d0fb4"
+BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="23c76b7f608e51258c6fca02aebeb5d588583149"
 BR2_LINUX_KERNEL_DEFCONFIG="bcm2709"
 BR2_LINUX_KERNEL_ZIMAGE=y
+
+# Install the DTB files, as the RPi2 uses the Device Tree
 BR2_PACKAGE_RPI_FIRMWARE=y
 BR2_PACKAGE_RPI_FIRMWARE_INSTALL_DTBS=y