ata: ahci_sunxi: Disable DIPM

DIPM is unsupported or broken on sunxi. Trying to enable the power
management policy med_power_with_dipm on an Allwinner A20 SoC based board
leads to immediate I/O errors and the attached SATA disk disappears from
the /dev filesystem. A reset (power cycle) is required to make the SATA
controller or disk work again. The A10 and A20 SoC data sheets and manuals
don't mention DIPM at all [1], so it's fair to assume that it's simply not
supported. But even if it was, it should be considered broken and best be
disabled in the ahci_sunxi driver.

[1] https://github.com/allwinner-zh/documents/tree/master/

Fixes: c5754b52

 ("ARM: sunxi: Add support for Allwinner SUNXi SoCs sata to ahci_platform")
Cc: stable@vger.kernel.org
Signed-off-by: Timo Sigurdsson <public_timo.s@silentcreek.de>
Tested-by: Timo Sigurdsson <public_timo.s@silentcreek.de>
Link: https://lore.kernel.org/r/20210614072539.3307-1-public_timo.s@silentcreek.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>