ArmVirtPkg/NorFlashQemuLib: disregard our primary FV

The primary FV contains the firmware boot image, which is not
runtime updatable in our case. So exposing it to the NOR flash
driver is undesirable, since it may attempt to modify the NOR
flash contents. It is also rather pointless, since we don't
keep anything there that we care to expose. (the SEC and PEI
phase modules are not executable from DXE context, and the
contents of the embedded DXE phase FV are exposed by the DXE
core directly via the FVB2 protocol)

So let's disregard the NOR flash block that covers the primary
FV.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>