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>

src/ec/google/chromeec/Kconfig

@@ -72,7 +72,7 @@ config EC_GOOGLE_CHROMEEC_SPI_WAKEUP_DELAY_US
 config EC_GOOGLE_CHROMEEC_SPI_CHIP
 	depends on EC_GOOGLE_CHROMEEC_SPI
 	hex
-	default 0
+	default 0x0
 
 config EC_GOOGLE_CHROMEEC_BOARDNAME
 	depends on EC_GOOGLE_CHROMEEC