OvmfPkg: BDS: drop custom boot timeout, revert to IntelFrameworkModulePkg's

OvmfPkg: BDS: drop custom boot timeout, revert to IntelFrameworkModulePkg's

PlatformBdsEnterFrontPage() already implements a keypress wait (for
entering the setup utility at boot) with a nice progress bar, only OVMF
has not been using it.

Removing our custom code and utilizing PlatformBdsEnterFrontPage()'s
builtin wait has the following benefits:

- It simplifies OVMF's BDS code.

- Because now we call PlatformBdsEnterFrontPage() unconditionally, it
  actually has a chance to look at the EFI_OS_INDICATIONS_BOOT_TO_FW_UI
  bit of the "OsIndications" variable, improving compliance with the UEFI
  specification. References:
  - https://bugzilla.redhat.com/show_bug.cgi?id=1153927
  - http://thread.gmane.org/gmane.comp.bios.tianocore.devel/10487

- The progress bar looks nice. (And it keeps the earlier behavior intact,
  when the user presses a key on the TianoCore splash screen.)

  In any case, we set the timeout to 0 (which doesn't show the progress
  bar and proceeds to the boot options immediately) in order to keep the
  boot time down.

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@16310 6f19259b-4bc3-4df7-8a09-765794883524