drm/amdgpu: use true and false for bool initialisations

Bool initialisation should use 'true' and 'false' values instead of 0
and 1.

Modify amdgpu_amdkfd_gpuvm.c to initialise variable is_imported
to false instead of 0.

Issue found with Coccinelle.

Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>