avr32: Kill CONFIG_MTD_PARTITIONS

This patch removes CONFIG_MTD_PARTITIONS in config files for avr32.
Because CONFIG_MTD_PARTITIONS was removed by commit
6a8a98b2

.

Signed-off-by: Eunbong Song <eunb.song@samsung.com>
Acked-by: Hans-Christian Egtvedt <hegtvedt@cisco.com>