google/rambi: Fix IASL warnings _CRS must return a value

The Touchpad and Touchscreen _CRS methods do not return an interrupt
value if the I2c busses that the devices are on are not in PCI mode.

Previously they didn't return any value if they weren't in PCI mode.
This patch has them return an empty resource template.

Fixes these warnings:
dsdt.aml 2813: Method (_CRS)
Warning  3115 -          ^ Not all control paths return a value (_CRS)
dsdt.aml 2813: Method (_CRS)
Warning  3107 -          ^ Reserved method must return a value
(Buffer required for _CRS)

dsdt.aml 2832: Method (_CRS)
Warning  3115 -          ^ Not all control paths return a value (_CRS)
dsdt.aml 2832: Method (_CRS)
Warning  3107 -          ^ Reserved method must return a value
(Buffer required for _CRS)

Change-Id: I02a29e56a513ec34a98534fb4a8d51df3b70a522
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12519
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/google/rambi/Kconfig

@@ -38,7 +38,4 @@ config HAVE_ME_BIN
 	bool
 	default n
 
-# TODO: Remove this when platform ASL is fixed
-config IASL_WARNINGS_ARE_ERRORS
-	def_bool n
 endif # BOARD_GOOGLE_RAMBI

src/mainboard/google/rambi/acpi/mainboard.asl

@@ -52,10 +52,13 @@ Scope (\_SB)
 
 		Method (_CRS)
 		{
-			/* Only return interrupt if I2C1 is PCI mode */
+			/* Return interrupt if I2C1 is PCI mode */
 			If (LEqual (\S1EN, 0)) {
 				Return (^RBUF)
 			}
+
+			/* Return empty resource template otherwise */
+			Return (ResourceTemplate() {})
 		}
 	}
 
@@ -76,10 +79,13 @@ Scope (\_SB)
 
 		Method (_CRS)
 		{
-			/* Only return interrupt if I2C6 is PCI mode */
+			/* Return interrupt if I2C6 is PCI mode */
 			If (LEqual (\S6EN, 0)) {
 				Return (^RBUF)
 			}
+
+			/* Return empty resource template otherwise */
+			Return (ResourceTemplate() {})
 		}
 	}
 }