kernel: Remove CONFIG_COMPAT

kernel: Remove CONFIG_COMPAT

This removes support for executing old 32 bit applications on 64 bit ARM
and MIPS kernels.
On OpenWrt we normally compile all the user space applications on our
own and do not support third party binary only modules especial not 32
bit applications on 64 bit CPUs.

This reduces the attack surface on such systems and should also save
some memory.

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