arm: mvebu: Add support for specifying VHV_Enable GPIO

VHV_Enable GPIO is required to enable during eFuse programming on Armada
SoCs not from 3700 family. Add support for enabling and disabling VHV pin
via GPIO during eFuse programming, when specified.

All details are in Marvell AN-389: ARMADA VHV Power document
(Doc. No. MV-S302545-00 Rev. C, August 2, 2016).

Note that due to HW Errata 3.6 eFuse erroneous burning (Ref #: HWE-3718342)
VHV power must be disabled while core voltage is off to prevent erroneous
eFuse programming.

This is specified in Marvell ARMADA 380/385/388 Functional Errata,
Guidelines, and Restrictions document
(Doc. No. MV-S501377-00 Rev. D, December 1, 2016).

Signed-off-by: Pali Rohár <pali@kernel.org>