NIOS2: fix kconfig unmet dependency warning for SERIAL_CORE_CONSOLE

SERIAL_CORE_CONSOLE depends on TTY so EARLY_PRINTK should also
depend on TTY so that it does not select SERIAL_CORE_CONSOLE
inadvertently.

WARNING: unmet direct dependencies detected for SERIAL_CORE_CONSOLE
  Depends on [n]: TTY [=n] && HAS_IOMEM [=y]
  Selected by [y]:
  - EARLY_PRINTK [=y]

Fixes: e8bf5bc7 ("nios2: add early printk support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>