gdb/testsuite/rocm: Add the hip_devices_support_debug_multi_process proc

gdb/testsuite/rocm: Add the hip_devices_support_debug_multi_process proc

It is not possible to debug multiple processes simultaneously on all
generations of AMDGPU devices.  As some tests will need to debug
multiple inferiors using AMDGPU devices, we need to ensure that all
devices available have the required capability.  Failing to do so would
result in GDB not being able to debug all inferiors properly.

Add the hip_devices_support_debug_multi_process helper function used to
ensure that all devices available can debug multiple processes.

Approved-By: Pedro Alves <pedro@palves.net>