i3c/master: introduce the mipi-i3c-hci driver

This adds basic support for hardware implementing the MIPI I3C HCI
specification. This driver is currently limited by the capabilities
of the I3C subsystem, meaning things like scheduled commands,
auto-commands and NCM mode are not yet supported.

This supports version 1.0 of the MIPI I3C HCI spec, as well as the
imminent release of version 1.1. Support for draft version 2.0 of the
spec is also largely included with the caveat that future adjustments
to this code are likely as the spec is still a work in progress.

This is also lightly tested as actual hardware is still very scarce,
even for HCI v1.0. Hence the EXPERIMENTAL tag. Further contributions
to this driver are expected once vendor implementations and new I3C
devices become available.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-i3c/20201111220510.3622216-3-nico@fluxnic.net