ArmVirtPkg: Add Kvmtool NOR flash lib

ArmVirtPkg: Add Kvmtool NOR flash lib

Kvmtool places the base address of the CFI flash in
the device tree it passes to UEFI. This library
parses the kvmtool device tree to read the CFI base
address and initialise the PCDs use by the NOR flash
driver and the variable storage.

UEFI takes ownership of the CFI flash hardware, and
exposes its functionality through the UEFI Runtime
Variable Service. Therefore, disable the device tree
node for the CFI flash used for storing the UEFI
variables, to prevent the OS from attaching its device
driver as well.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@arm.com>