hw/arm: introduce xenpvh machine

hw/arm: introduce xenpvh machine

Add a new machine xenpvh which creates a IOREQ server to register/connect with
Xen Hypervisor.

Optional: When CONFIG_TPM is enabled, it also creates a tpm-tis-device, adds a
TPM emulator and connects to swtpm running on host machine via chardev socket
and support TPM functionalities for a guest domain.

Extra command line for aarch64 xenpvh QEMU to connect to swtpm:
    -chardev socket,id=chrtpm,path=/tmp/myvtpm2/swtpm-sock \
    -tpmdev emulator,id=tpm0,chardev=chrtpm \
    -machine tpm-base-addr=0x0c000000 \

swtpm implements a TPM software emulator(TPM 1.2 & TPM 2) built on libtpms and
provides access to TPM functionality over socket, chardev and CUSE interface.
Github repo: https://github.com/stefanberger/swtpm
Example for starting swtpm on host machine:
    mkdir /tmp/vtpm2
    swtpm socket --tpmstate dir=/tmp/vtpm2 \
    --ctrl type=unixio,path=/tmp/vtpm2/swtpm-sock &

Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>