dm: ahci: Drop use of probe_ent

dm: ahci: Drop use of probe_ent

With driver model we cannot have static data or assume that there is only
one device of each time. Adjust the code so that 'probe_ent' is not needed
with driver model. Add a new ahci_init_dm() function which can init AHCI
for driver model without re-allocating the uclass data. Move over the only
existing driver to use this new function.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>