configs: at91: sam9x60_curiosity: Sync both defconfig variants

configs: at91: sam9x60_curiosity: Sync both defconfig variants

The board has two SD card slots and we have two defconfigs for booting
from either the first (micro SD) named 'sam9x60_curiosity_mmc_defconfig'
or the second (full size SD) named 'sam9x60_curiosity_mmc1_defconfig'.
For comparable Microchip boards (sama5d27-som1-ek, sama5d29-curiosity,
sama7g5ek) with two card slots the defconfigs only differ in BOOTARGS,
BOOTCOMMAND, and ENV_FAT_DEVICE_AND_PART and the same should be the case
for sam9x60_curiosity.

Here the 'mmc1' config has more options enabled to support the raw NAND
flash populated on the board, so the 'mmc' config (for mmc0) was adapted
by enabling additional options, instead of removing options from mmc1.

The 'mem=128M' argument can be dropped from kernel command line, because
it is redundant to memory node in dts in both Linux and U-Boot:

        memory@20000000 {
                reg = <0x20000000 0x8000000>;
        };

Signed-off-by: Alexander Dahl <ada@thorsis.com>