exshields: board support based on exynos 5 dual

* Add exshields board support based on
  Samsung Exynos 5 Dual
* Add common settings from smdk5250 reference boards
* Clean up pmic settings only add support for S5M8767

Signed-off-by: Adrian Alonso <aalonso@htdevices.com>
exshields: config setting for exshields board

* Add config settings for exshields board
* Set MACH_TYPE 3992, kernel-exynos should
  use this ID
* Set common exynos5250 settings

Signed-off-by: Adrian Alonso <aalonso@htdevices.com>
boards: add exshields config option

* Add exhields board config option

Signed-off-by: Adrian Alonso <aalonso@htdevices.com>
sd_fuse: add helper script to flash uboot

* Add sd_fuse helper script to flash uboot
  into sdcard

Signed-off-by: Adrian Alonso <aalonso@htdevices.com>