macintosh: Remove dependency on IDE_GD_ATA if ADB_PMU_LED_DISK is selected

We can use the front led of powerbooks/ibooks to visualize disk activity
without the deprecated IDE_GD_ATA.

Signed-off-by: Elimar Riesebieter <riesebie@lxtec.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>