EXYNOS: Move files from board/samsung to arch/arm

This patch performs the following:

1) Convert the assembly code for memory and clock initialization to C code.
2) Move the memory and clock init codes from board/samsung to arch/arm
3) Creat a common lowlevel_init file across Exynos4 and Exynos5. Converted
   the common lowlevel_init from assembly to C-code
4) Made spl_boot.c and tzpc_init.c common for both exynos4 and exynos5.
5) Enable CONFIG_SKIP_LOWLEVEL_INIT as stack pointer initialisation is already
   done in _main.
6) exynos-uboot-spl.lds made common across SMDKV310, Origen and SMDK5250.

TEST: Tested SD-MMC boot on SMDK5250 and Origen.
      Tested USB and SPI boot on SMDK5250
      Compile tested for SMDKV310.

Signed-off-by: Rajeshwari Shinde <rajeshwari.s@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>