all targets: remove all =m kernel config symbols

modules build during the kernel compile phase are ignored anyway,
all modules should be built using KernelPackage in
package/kernel/linux/modules/*
selecting the appropriate config symbols there rather than in
target/linux/*/config-*

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43842 3c298f89-4303-0410-b956-a3cf2f4a3e73