amdkfd: Disable support for 32-bit user processes

This patch checks if the process that opens the /dev/kfd device is 32-bit
process. If so, it returns -EPERM and prints a warning message in dmesg.

This is done to prevent 32-bit user processes from using amdkfd, and hence, HSA
features.

AMD's HSA userspace stack will also support only 64-bit processes on Linux.

Reviewed-by: Alexey Skidanov <alexey.skidanov@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>