ARM: exynos_defconfig: Enable GPIO buttons and RTC drivers

Many of the boards use GPIO-mapped buttons for generic input.
For Arndale board, these buttons also serve as wakeup source.

And the issues reported in commit 522ccdb6 ("ARM: dts:
Disable the RTC by default on exynos5") are no longer reproduced
on EXYNOS5250 based systems. Hence it would be better to re-enable
RTC support for EXYNOS5250.

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
[mturquette@linaro.org: ack on RTC enabling]
Acked-by: Mike Turquette <mturquette@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>