defconfig: Enable default-key driver for msm8937_32

This flag is needed for Metadata encryption to work:
CONFIG_DM_DEFAULT_KEY=y.
Test: 1. Device bootup with Metadata Encryption Enabled.
      2. Randomness test.
      3. vts_kernel_encryption_tests

Change-Id: I27ce51c2a2d52826caf0190603f91949fa89c824
Signed-off-by: Vaibhav Agrawal <vagrawa@codeaurora.org>