OvmfPkg: BDS: don't overwrite the BDS Front Page timeout

OvmfPkg: BDS: don't overwrite the BDS Front Page timeout

The PlatformBdsEnterFrontPage() function's first parameter,
"TimeoutDefault", determines the behavior of the setup utility:

- If (TimeoutDefault == 0), then the usual boot order is to be acted upon
  immediately.

- If (TimeoutDefault == 0xFFFF), then the setup utility is entered
  unconditionally.

- If (0 < TimeoutDefault && TimeoutDefault < 0xFFFF), then the
  PlatformBdsEnterFrontPage() function displays a progress bar, waiting
  for TimeoutDefault seconds. If the user presses a key, then the setup
  utility is entered, otherwise the normal boot option processing takes
  place.

The TimeoutDefault parameter is supposed to be set from

  gEfiIntelFrameworkModulePkgTokenSpaceGuid.PcdPlatformBootTimeOut

which has the following (matching) documentation in
"IntelFrameworkModulePkg/IntelFrameworkModulePkg.dec":

  The number of seconds that the firmware will wait before initiating the
  original default boot selection.
  A value of 0 indicates that the default boot selection is to be
  initiated immediately on boot.
  The value of 0xFFFF then firmware will wait for user input before
  booting.

OVMF does this actually -- see the Timeout variable in
PlatformBdsPolicyBehavior() -- but right before calling
PlatformBdsEnterFrontPage(), OVMF hardwires TimeoutDefault to 0xFFFF.

This has been acceptable until now, because OVMF implements its own "wait
for keypress at the splash screen" logic in PlatformBdsPolicyBehavior(),
completely avoiding the progress bar mentioned above. OVMF only calls
PlatformBdsEnterFrontPage() when the user presses a key during its own
"splash screen wait", and *then* it indeed makes sense to enter the setup
utility unconditionally.

However, even that way, the

  Timeout = 0xffff;

assignment is superfluous, because 0xFFFF is already the default value of
PcdPlatformBootTimeOut in "IntelFrameworkModulePkg.dec", and OvmfPkg
doesn't override it in its DSC files.

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@16307 6f19259b-4bc3-4df7-8a09-765794883524