Kconfig: Update default hex values to start with 0x

Kconfig hex values don't need to be in quotes, and should start with
'0x'.  If the default value isn't set this way, Kconfig will add the
0x to the start, and the entry can be added unnecessarily to the
defconfig since it's "different" than what was set by the default.

A check for this has been added to the Kconfig lint tool.

Change-Id: I86f37340682771700011b6285e4b4af41b7e9968
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/16834
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/src/mainboard/google/gru/Kconfig b/src/mainboard/google/gru/Kconfig
index 3150839..41e81055 100644
--- a/src/mainboard/google/gru/Kconfig
+++ b/src/mainboard/google/gru/Kconfig
@@ -65,7 +65,7 @@
 
 config EC_GOOGLE_CHROMEEC_SPI_BUS
 	hex
-	default 5
+	default 0x5
 
 config BOOT_DEVICE_SPI_FLASH_BUS
 	int
@@ -73,7 +73,7 @@
 
 config DRIVER_TPM_I2C_BUS
 	hex
-	default 0
+	default 0x0
 
 config DRIVER_TPM_I2C_ADDR
 	hex