Generalize output banner write routine
Generalize output banner write routine

Initial display output is replayed to vga/vnc display, similar facility
will be needed for virtio-serial console as the enumeration would only
happen during PCI discovery.

Generalize the write routine that could be used accordingly for
virtio-serial driver as well.

Signed-off-by: Nikunj A Dadhania <e2f4a5db9b4735182a88051d1e7a3599f9eac9db@linux.vnet.ibm.com>
Signed-off-by: Alexey Kardashevskiy <ac1fc56530d7d037e1ea666f130daca22d72f964@ozlabs.ru>

open-power-host-os/slof,open-power-host-os/slof,open-power-host-os/slof,qemu/SLOF,stefanberger/SLOF-tpm,qemu/SLOF,aik/SLOF,qemu/SLOF,stefanberger/SLOF-tpm,open-power-host-os/slof,stefanberger/SLOF-tpm,aik/SLOF,aik/SLOF