ANDROID: arm64: temporarily mark ARM64_SW_TTBR0_PAN as BROKEN

The backport of ARM64 THREAD_INFO_IN_TASK is about to take away
init_thread_info.  This will break the build for kernels with
CONFIG_ARM64_SW_TTBR0_PAN=y.  Make this option depend on BROKEN until we
repair the damage later in the patchstack.

Change-Id: I383f1a0529f8b893c5f70dbb471fe25b1db1414e
Signed-off-by: Greg Hackmann <ghackmann@google.com>