drm/amdgpu: add CONFIG_GCOV_PROFILE_AMDGPU Kconfig option

drm/amdgpu: add CONFIG_GCOV_PROFILE_AMDGPU Kconfig option

Add a Kconfig option to enable GCOV code coverage profiling for the
amdgpu driver, following the established upstream pattern used by
CONFIG_GCOV_PROFILE_FTRACE (kernel/trace), CONFIG_GCOV_PROFILE_RDS
(net/rds), and CONFIG_GCOV_PROFILE_URING (io_uring).

This allows CI systems to enable amdgpu code coverage entirely via
.config (e.g., scripts/config --enable GCOV_PROFILE_AMDGPU) without
manually editing the amdgpu Makefile. The option depends on both
DRM_AMDGPU and GCOV_KERNEL, defaults to n, and is therefore never
enabled in production or distro builds.

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>