accel/amdxdna: Revise device bo creation and free

The device bo is allocated from the device heap memory. (a trunk of
memory dedicated to device)

Rename amdxdna_gem_insert_node_locked to amdxdna_gem_heap_alloc
and move related sanity checks into it.

Add amdxdna_gem_dev_obj_free and move device bo free code into it.

Calculate the kernel virtual address of device bo by the device
heap memory address and offset.

Reviewed-by: Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://lore.kernel.org/r/20250616091418.2605476-1-lizhi.hou@amd.com