ARM: shmobile: Update KZM9D dts command line

Update the KZM9D DTS command line to remove following cruft:
 - console=tty0 - no graphic support upstream anyway
 - earlyprintk= - not supported by the 8250-em driver anyway
 - mem= - this is provided via DT anyway

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>