ARM: at91: dt: add Calao USB-A9G20 low power version

the low power version have a mmc-spi

eanble mmc-spi and RV3029C2 RTC in at91_dt_defconfig

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
ARM: at91: drop non DT: Calao USB-A96x

as now we have full DT support of those board

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>