mtd: onenand: remove s5pc100 related onenand codes

This patch removes s5pc100 related onenand codes because of no more
support for S5PC100 SoC in mainline.

Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>