can: mcp25xxfd: Add Microchip MCP25XXFD CAN-FD driver infrastructure

This commit adds basic driver support for the Microchip MCP25XXFD
CAN-FD controller series. This driver currently supports MCP2517FD as the
target controller.

The MCP2517FD is capable of transmitting and receiving standard data
frames, extended data frames, remote frames and Can-FD frames.
The MCP2517FD interfaces with the host over SPI.

This commit provides basic driver functionality such as setting up clocks,
regulators and the infrastructure for the CAN.

Datasheet:
* http://ww1.microchip.com/downloads/en/DeviceDoc/20005688A.pdf
Reference manual:
* http://ww1.microchip.com/downloads/en/DeviceDoc/20005678A.pdf
Errata:
* http://ww1.microchip.com/downloads/en/DeviceDoc/MCP2517FD-Silicon-Errata-and-Data-Sheet-Clarification-DS80000792A.pdf



Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
[mani: trimmed the gpio part and done some cleanups]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>