ARM: 5815/1: SA1100: h3100/h3600: remove now unused assign_h3600_egpio handlers

As all users of assign_h3600_egpio now converted to gpiolib, we
can safely remove all assign_h3600_egpio handling code and
definitions.

Signed-off-by: Dmitry Artamonow <mad_soft@inbox.ru>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>