ec/lenovo/h8: Use older syntax for bit shift

Currently, when using `iasl` 20140926-32 [Oct  1 2014] from Debian 8
(Jessie/stable), the build of the Lenovo X60 fails due to syntax errors.

ASL 2.0 supports `<<`. For consistency, right now, coreboot still uses
the old syntax. So use `ShiftLeft` instead, which also fixes the build
issue with older ASL compilers.

Change-Id: Id7e309c31612387da3920cf7d846b358ac2bdc71
Signed-off-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-on: https://review.coreboot.org/18520
Tested-by: build bot (Jenkins)
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/ec/lenovo/h8/acpi/ec.asl

@@ -363,7 +363,7 @@ Device(EC)
 		/* Report tablet mode switch state */
 		Method (MHKG, 0, NotSerialized)
 		{
-			Return (TBSW << 3)
+			Return (ShiftLeft(TBSW, 3))
 		}
 		/* Mute audio */
 		Method (SSMS, 1, NotSerialized)