ipq806x: switch AP148 to using SMEM based MTD parser

ipq806x: switch AP148 to using SMEM based MTD parser

*Enable SMEM MTD parser and its dependencies (SMEM & HW spinlocks) in
 the kernel config
*Replaces the MTD layout in DT by the dynamic layout provided by the
 SMEM parser for AP148

Using the OF based parser is still possible on platforms which have a
fixed MTD partition layout.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46658 3c298f89-4303-0410-b956-a3cf2f4a3e73