src/*: Specify type of DIMM_MAX once

Specify the type of the `DIMM_MAX` Kconfig symbol once.

Change-Id: I2e86baaa8bd50c7b82c399fde5dcea05da6b4307
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57258
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Crawford <tcrawford@system76.com>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>

src/mainboard/libretrend/lt1000/Kconfig

@@ -31,7 +31,6 @@ config VGA_BIOS_ID
 	default "8086,1916"
 
 config DIMM_MAX
-	int
 	default 2
 
 config DIMM_SPD_SIZE