ARM: at91/dt: remove bootargs

Passing earlyprintk in the bootargs may crash the board as it depends on
having a sane DEBUG_UART_PHYS configured which is not always the case.

Also remove ignore_loglevel

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>