ArmPlatformPkg/PrePi: allow unicore version to be used on MP hardware

ArmPlatformPkg/PrePi: allow unicore version to be used on MP hardware

When combining UEFI firmware built from Tianocore with ARM Trusted
Firmware running in EL3, it is the responsibility of ATF that only
a single core enters the UEFI firmware in EL2, and the remaining cores
are released directly to the OS via PSCI SMC calls.

In this case, we don't need the MpCore flavor of PrePi or PrePeiCore,
but the UniCore flavor currently checks the CPU identification registers
directly, and refuses to proceed if the boot CPU is part of a MpCore
system.

So drop the ASSERT()'s that implement this check.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>