ARM: dts: vexpress: use standard gpio bindings for sys_{led,mci,flash}

ARM: dts: vexpress: use standard gpio bindings for sys_{led,mci,flash}

Commit 2cff6dba57b7 ("ARM: dts: vexpress: fix node name unit-address presence warnings")
removed the unit address as there was no associated reg property in
these sysreg nodes.

Also the latest DTC throws warnings for character '_' in the node names.

Warning (node_name_chars_strict): /sysreg@10000/sys_led: Character '_' not recommended in node name
Warning (node_name_chars_strict): /sysreg@10000/sys_mci: Character '_' not recommended in node name
Warning (node_name_chars_strict): /sysreg@10000/sys_flash: Character '_' not recommended in node name

The correct way to fix this as well as the original unit-address presence
warnings is to use the standard gpio controller binding and specify the
reg properties as per the hardware as it was before.

However note that Vexpress sysreg MFD driver will still continue to use
the hardcoded values for compatibility reasons.

Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Suggested-by: Rob Herring <robh@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>