Add basic MSL support for i.MX6SLL.

The i.MX 6SoloLiteLite application processors are NXP's latest
additions to a growing family of multimedia-focused products
offering high-performance processing optimized for lowest power
consumption. The i.MX 6SoloLiteLite processors feature NXP's advanced
implementation of the ARM Cortex-A9 core, which can be interfaced
with LPDDR3 and LPDDR2 DRAM memory devices.
Signed-off-by: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>