ARM: DT: APQ8064: Add node for ps_hold function in pinctrl

This patch adds DT support to configure GPIO_78 as function ps_hold
on apq8064.

CC: Rob Herring <robh+dt@kernel.org>
CC: Pawel Moll <pawel.moll@arm.com>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Ian Campbell <ijc+devicetree@hellion.org.uk>
CC: Kumar Gala <galak@codeaurora.org>
CC: devicetree@vger.kernel.org
CC: linux-arm-kernel@lists.infradead.org
Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Kumar Gala <galak@codeaurora.org>