platform/mellanox: mlxreg-lc: Add initial support for Nvidia line card devices

Provide support for the Nvidia MSN4800-XX line cards for MSN4800
Ethernet modular switch system, providing a high performance switching
solution for Enterprise Data Centers (EDC) for building Ethernet based
clusters, High-Performance Computing (HPC) and embedded environments.
Initial version provides support for line card type MSN4800-C16. This
type of line card is equipped with:
- Lattice CPLD device, used for system and ports control.
- four Nvidia gearbox devices, used for port splitting.
- FPGA device, used for gearboxes management.
- 16x100G QSFP28 ports.
- hotpswap controllers, voltage regulators, analog-to-digital
  convertors, nvram devices.
- status LED.

During initialization driver creates:
- line card's I2C tree through "i2c-mux-mlxcpd" driver.
- line card's LED objects through "leds-mlxreg" driver.
- line card's CPLD register space input / output "hwmon" attributes for
  line control and monitoring through "mlxreg-io" driver. These
  attributes provide CPLD and FPAG versioning, control for upgradable
  components burning, NVRAM devices write protection, line card
  revision, line card power consuming, line card reset cause
  indication, etcetera.

Lattice CPLD device and nvram devices are feeding from auxiliary power
domain and accessible, when line card is powered off. These devices
are connected by line card driver probing routine, invoked after line
card security verification is done by hardware and event lc#n_verified
is received for line card located in slot #n.

Gearboxes, FPGA, hotpswap controllers, voltage regulators,
analog-to-digital convertors are feeding from main power domain. These
devices are connected after power good event "lc#n_powered" is received
for line card located in slot #n.

The driver 'mlxreg-lc' is driven by 'mlxreg-hotplug' driver following
relevant "hotplug" events.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Link: https://lore.kernel.org/r/20211002093238.3771419-8-vadimp@nvidia.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>