msm: kgsl: Make secure memory depend on QCOM_SECURE_BUFFER

Secure memory uses a helper driver to lock memory in the hypervisor. The
helper driver is selectable at compile time (CONFIG_QCOM_SECURE_BUFFER)
Any attempts to allocate secure memory without the dependent support
will return -ENODEV which the kernel and user drivers should know how to
handle safely.

Change-Id: Ic0dedbadbde75ce8856a677d7c7793cda0c2c727
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>