ARM: at91: sam9n12: enable kernel uncompress info output

The sam9n12 use the same array usart as sam9x5, add it which will
enable output kernel uncompress info:
---8>---
Uncompressing Linux... done, booting the kernel.
---<8---

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>