drivers: console: uart_mux: Initial UART muxing support

Create support for muxed UARTs which are attached to a real
UART and which use GSM 07.10 muxing protocol to create virtual
channels that can be run on top of the real UART.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
diff --git a/scripts/sanity_chk/sanitylib.py b/scripts/sanity_chk/sanitylib.py
index 34b1e70..9ca177c 100644
--- a/scripts/sanity_chk/sanitylib.py
+++ b/scripts/sanity_chk/sanitylib.py
@@ -895,6 +895,7 @@
         "ccm_data",
         "usb_descriptor",
         "usb_data", "usb_bos_desc",
+        "uart_mux",
         'log_backends_sections',
         'log_dynamic_sections',
         'log_const_sections',