doc/configuration: add strip_timestamp to UBootDriver

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>

Author: threexc

doc/configuration.rst

@@ -1925,6 +1925,7 @@ Arguments:
   - boot_commands (dict, default={}): boot commands by name for LinuxBootProtocol boot command
   - login_timeout (int, default=30): timeout for login prompt detection in seconds
   - boot_timeout (int, default=30): timeout for initial Linux Kernel version detection
+  - strip_timestamp (bool, default=False): strip timestamps prepended to console when present
 
 SmallUBootDriver
 ~~~~~~~~~~~~~~~~