greybus: arche-apb-ctrl: Set wake_detect gpio to low initially

This patch enables handshaking of AP and SVC using wake_detect
gpio (WD_8A and WD_8B).
Note that WAKE_DETECT polarity is active-high, so in order to
enable handshaking between AP <=> SVC, we need to set wake_detect
gpio to low initially, so that driver can send WAKE_DET signal
(active-high) to SVC and then SVC can send back WAKE_MOD signal
(active-low).
And on reception of WAKE_MOD signal, driver would bring respective
APB out of reset.

  WD_8A => APB1
  WD_8B => APB2

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>