configs/bananapi_m1_plus_defconfig: select custom headers

Board used custom Kernel but did not specify
custom headers. This broke the build when
Linux 5.11 was added in d2fe9c6.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1089053980

Signed-off-by: Filip Skoneczny <fskoneczny@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/bananapi_m1_plus_defconfig

@@ -2,6 +2,7 @@ BR2_arm=y
 BR2_cortex_a7=y
 BR2_ARM_FPU_NEON_VFPV4=y
 BR2_GLOBAL_PATCH_DIR="board/sinovoip/m1-plus/patches"
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_5_10=y
 BR2_TARGET_GENERIC_HOSTNAME="bananapi"
 BR2_TARGET_GENERIC_ISSUE="Welcome to Banana Pi!"
 BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y