misc: amd-sbi: Clarify that this is a BMC driver

Add a sentence to the driver description to clarify that the sbrmi-i2c
driver is intended to run on the BMC and not on the managed node. Add
platform dependencies accordingly.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Link: https://lore.kernel.org/r/5c9f7100-0e59-4237-a252-43c3ee4802a2@amd.com
Link: https://patch.msgid.link/20251016155040.0e86c102@endymion


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>