matrix: Enforce kernel requirements in OTA only when flag is set.

Enforce only when PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS
is set. If a device does want to require kernel configs, it has to
provide info for new kernel in OTA package.
Bug: 111840577
Test: build and manual inspection

Change-Id: I36b3fcd9d14a9795aaf8d020bba6180c5e8681d1