docs: interconnect.rst: add it to the driver-api guide

This is intended for Kernel hackers audience.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by: Georgi Djakov <georgi.djakov@linaro.org>

Documentation/driver-api/index.rst

@@ -36,6 +36,7 @@ available subsections can be seen below.
    i2c
    ipmb
    i3c/index
+   interconnect
    hsi
    edac
    scsi