FROMGIT: dt-bindings: cpufreq: add virtual cpufreq device

Adding bindings to represent a virtual cpufreq device.

Virtual machines may expose MMIO regions for a virtual cpufreq device
for guests to read performance information or to request performance
selection. The virtual cpufreq device has an individual controller for
each performance domain. Performance points for a given domain can be
normalized across all domains for ease of allowing for virtual machines
to migrate between hosts.

Bug: 284367589
Test: Boot up with compatible VMM backend emulation
Link: https://lore.kernel.org/all/20240919000837.1004642-2-davidai@google.com/
(cherry picked from commit 984638e4
 git://git.kernel.org/pub/scm/linux/kernel/git/vireshk/pm.git

 cpufreq/arm/linux-next)
Change-Id: Ic67335c69a4b584e9f5008e02f87b4179002375e
Co-developed-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: David Dai <davidai@google.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>