mfd: remove htc-pasic3 driver

The htc-pasic3 MFD device was only used in the PXA magician
machine that is now removed, so this can be recycled as well.

Cc: Lee Jones <lee@kernel.org>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>