s5p_mmc: support 8-bit bus width

This Patch do support 8-bit bus width for s5p
So we add parameter for bus_width (in s5p_mmc_init(), s5p_mmc_initialize())
If want to use 8-bit bus width, only change (0, 8) instead of (0, 4).

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>