drivers/ipmi: Add chip ops

* Add chips ops for IPMI KCS.
* Get IPMI version over KCS.
* Generates ACPI SPMI table for IPMI KCS.
* Generates SMBIOS type 38 for IPMI KCS.
* Generates ACPI SPMI device for IPMI KCS on LPC device.
* Add documentation

To use this driver on BMC that support KCS on I/O:

1. Add an entry to the devicetree.cb:

 chip drivers/ipmi
    device pnp ca2.0 on end         # IPMI KCS
 end

2. Select IPMI_KCS in Kconfig.
3. (Optional) enable LPC I/O decode for the given address.

Tested on Wedge100s.

Change-Id: I73cbd2058ccdc5395baf244f31345a85eb0047d7
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33255
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

Documentation/index.md

@@ -175,6 +175,7 @@ Contents:
 * [Native Graphics Initialization with libgfxinit](gfx/libgfxinit.md)
 * [Display panel-specific documentation](gfx/display-panel.md)
 * [Architecture-specific documentation](arch/index.md)
+* [Platform independend drivers documentation](drivers/index.md)
 * [Northbridge-specific documentation](northbridge/index.md)
 * [System on Chip-specific documentation](soc/index.md)
 * [Mainboard-specific documentation](mainboard/index.md)