arm: am335x: add Kconfig range attribute to prevent invalid CONS_INDEX

The help message in board/ti/am335x/Kconfig says AM335x has
6 UARTs, so the valid number for CONFIG_CONS_INDEX is from 1 to 6.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
1 file changed