defconfig: arm: Disable mmc clock gating on SDM670

Disable mmc clock gating on SDM670 since with gating enabled
mmc cmdq controller is getting struck in few corner cases.

Once cmdq issues are fixed will re-enable the gating.

Change-Id: I222b704e5c4e5b85333ea39f802bb9cc074315e5
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>