kirkwood: add missing kernel symbol

The query for ARMADA_THERMAL is stalling the kconfig process and as long as we
do not package it, simply disable the symbol.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/kirkwood/config-4.4

@@ -38,6 +38,7 @@ CONFIG_ARM_L1_CACHE_SHIFT=5
 # CONFIG_ARM_MVEBU_V7_CPUIDLE is not set
 CONFIG_ARM_PATCH_PHYS_VIRT=y
 # CONFIG_ARM_THUMB is not set
+# CONFIG_ARMADA_THERMAL is not set
 CONFIG_ATAGS=y
 CONFIG_AUTO_ZRELADDR=y
 CONFIG_BLK_DEV_SD=y