qseecom: Fix QSEECOM_IOCTL_UNLOAD_EXTERNAL_ELF_REQ kernel crash

Fixes the kernel crash occuring with IOCTL_UNLOAD_EXTERNAL_ELF_REQ
ioctl by adding unavailable client type to qseecom_client_handle_type
enum, which is required in the driver during qseecom_release().

Change-Id: I73b817255149ffc4a808852feb2954a0ba3c317f
CRs-fixed: 508253
Signed-off-by: AnilKumar Chimata <anilc@codeaurora.org>