SignedCapsulePkg/PlatformFlashAccessLib: Add progress API

SignedCapsulePkg/PlatformFlashAccessLib: Add progress API

https://bugzilla.tianocore.org/show_bug.cgi?id=801

Add a new API to the PlatformFlashAccessLib that passes
in an optional Progress() function along with a start and
end percentage to call the Progress() function with.
If the Progress() function is not NULL, then it is the
Progress() function that was passed into the Firmware
Management Protocol SetImage() services and is used
to update the user on the progress as a firmware device
is updated with a firmware image.

Implementations of the PlatformFlashAccessLib are
recommended to call the Progress() function as work
is performed to update to contents of a firmware
storage device.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>