defconfig: msm8974: Enable Kickstart and diag bridge drivers

Kickstart and diag bridge are used for flashless boot and debugging
when external modem is connected over USB/HSIC interface.

Change-Id: Iaf02425a285504e206cdfa2a2eb6555602c054a8
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>