ARM: dts: correct the mmc0 capability string for exynos Peach boards

MMC capability for HS200 is parsed in mmc/core/host.c as
dts string "mmc-hs200-1_8v".

This patch corrects the dts string for Exynos5420 based peach-pit
and Exynos5800 based peach-pi boards.

Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>