ArmVirtPkg/ArmVirtPrePiUniCoreRelocatable: deal with relaxed XIP alignment

ArmVirtPkg/ArmVirtPrePiUniCoreRelocatable: deal with relaxed XIP alignment

Commit b89919ee8f8c ("BaseTools AARCH64: override XIP module linker
alignment to 32 bytes") updated the various AARCH64 toolchain definitions
to allow SEC, PEI_CORE and PEIM modules to be built with minimal alignment
requirements even when using the AArch64 small code model which normally
requires 4 KB section alignment.

This involves conversion of ADRP instructions into ADR instructions, which
can only be done reliably if the ELF and the PE/COFF sections appear at
the same offset modulo 4 KB.

The ArmVirtPrePiUniCoreRelocatable linker script did not yet take this
into account, so update it by starting the .text section at the next
appropriately aligned offset PECOFF_HEADER_SIZE bytes into the image.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>