ipq806x: clean-up kernel config file

Options that used to be in target config have been added to the generic
config file, so remove them.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@45255 3c298f89-4303-0410-b956-a3cf2f4a3e73