OvmfPkg/PlatformBootManagerLib: process "-kernel" before boot devices

OvmfPkg/PlatformBootManagerLib: process "-kernel" before boot devices

This improves the UEFI boot time for VMs that have "-kernel", many disks
or NICs, and no "bootindex" properties.

(Unlike in ArmVirt commit 23d04b58e27b, in OvmfPkg commit 52fba28994e9 we
introduced TryRunningQemuKernel() right from the start *after*
BdsLibConnectAll(). Therefore, unlike in patch
'ArmVirtPkg/PlatformBootManagerLib: return to "-kernel before boot
devices"', we adopt the logic as new in this patch.)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Gabriel Somlo <gsomlo@gmail.com>