MIPS: Loongson: Add basic Loongson 2F support

Loongson 2F has built-in DDR2 and PCI-X controller. The PCI-X controller
has a programming interface similiar to the the FPGA northbridge used on
Loongson 2E.

The main differences between Loongson 2E and Loongson 2F include:

1. Loongson 2F has an extra address window configuration module, which
   is used to map CPU address space to DDR or PCI address space, or map
   the PCI-DMA address space to DDR or LIO address space.

2. Loongson 2F supports 8 levels of software configurable CPu frequency
   which can be configured in the LOONGSON_CHIPCFG0 register.  The coming
   cpufreq and standby support are based on this feature.

Loongson.h abstracts the modules and corresponding methods are abstracted.

Add other Loongson-2F-specific source code including gcc 4.4 support, PCI
memory space, PCI IO space, DMA address.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>