OvmfPkg: PlatformDxe: connect RouteConfig() to platform data

OvmfPkg: PlatformDxe: connect RouteConfig() to platform data

Establish the full stack of conversions when modifying the platform
configuration:

       ConfigResp            -- form engine / HII communication
            |
     [ConfigToBlock]
            |
            v
     MAIN_FORM_STATE         -- binary representation of form/widget state
            |
[FormStateToPlatformConfig]
            |
            v
     PLATFORM_CONFIG         -- accessible to DXE and UEFI drivers
            |
   [PlatformConfigSave]
            |
            v
  UEFI non-volatile variable -- accessible to external utilities

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15375 6f19259b-4bc3-4df7-8a09-765794883524