ARM: SAMSUNG: Fix build without SDHCI controllers for S3C64XX

This patch fixes the following compilation problem if only NCP machine
is selected:

arch/arm/mach-s3c64xx/s3c6410.c: In function 's3c6410_map_io':
arch/arm/mach-s3c64xx/s3c6410.c:51: error: implicit declaration of function 's3c6410_default_sdhci2'

And also adds missed 's3c6400_default_sdhci2'.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
[kgene.kim@samsung.com: minor title fix and added comments]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>