common/octeontx2: add build infrastructure and HW definition

Add the make and meson based build infrastructure along with
HW definition header file.

This patch adds skeleton otx2_mbox.c file to make sure
all header files are intact, subsequent patches add content
to otx2_mbox.c

This patch also updates CONFIG_RTE_MAX_VFIO_GROUPS
value to 128 as the system can have up to 128 PFs/VFs.
For octeontx2 meson build target, CONFIG_RTE_MAX_VFIO_GROUPS
defined as 128 so no additional changes required.

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>