ARM: imx_v6_v7_defconfig: Remove CONFIG_DEFAULT_MMAP_MIN_ADDR

By default CONFIG_DEFAULT_MMAP_MIN_ADDR is 4096 and can also be changed via
/proc/sys/vm/mmap_min_addr if needed.

Quoting Russell King (http://marc.info/?l=linux-arm-kernel&m=134401593807820&w=2

):

"4096 is also fine for ARM too.  There's not much point in having
defconfigs change it - that would just be pure noise in the config
files."

,so remove CONFIG_DEFAULT_MMAP_MIN_ADDR from the defconfig file.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>