ARM: EXYNOS4: Enhancement of System MMU driver

This patch includes the following enhancements for System MMU:
- Enhanced readability
- Removal of unused data structures or their members
- Simplified function definitions
- Corrections of some logical errors
- Full compliance with Linux coding style
- Simpler way of registering callback functions of System MMU faults

Signed-off-by: KyongHo Cho <pullip.cho@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>