IntelFsp2Pkg/FspSecCore: Do not hang when bootloader IDT is larger

The current logic in FspSecCore is when the size of IDT created
by the bootloader is larger than the size of IDT that's going to be created
by FSP, CpuDeadLoop() is hit.

Change PcdFspMaxInterruptSupported from 34 to 255 to avoid such case.

Even when the PCD is overriden to a small value, the dead-loop is
not necessary. The patch updates the logic to only copy
the first part of the IDT entries when bootloader's IDT is larger.
A warn is printed in the debug log when such case happens.

The change addresses a boot hang in FSP API mode introduced by
commit 3454d7ab41.

Signed-off-by: Ray Ni <ray.ni@intel.com>