ARM: dts: add sd card detect definition for msm8994

PM8994 gpio 8 is used for sd card detection and the card present state
is active low. Update the sdhc node that is used for sd card with this
information.

Change-Id: I0bcef93b5f919403b7ab593ec6f48f65a0c81dae
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>