kernel: Deactivate CONFIG_COMPAT_BRK

CONFIG_COMPAT_BRK disables the heap randomization which is only needed
for very old and ancient user space applications, I am not aware that we
run any of these, just deactivate this option for these targets to allow
heap randomization.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>