arch/arm: drop ARM(7TDMI/720T/740T) support

arch/arm: drop ARM(7TDMI/720T/740T) support

The toolchain currently doesn't build for nommu ARM and is in need of
serious work.
Problem is there are no emulation targets and real ARM(7TDMI/720T/740T)
hardware that's capable of running linux (enough memory, having a
memory controller...) is VERY rare and uses very old versions to
make it usable.

The ARM nommu focus should go into Cortex M series processors that are
obtainable at reasonable cost on modern hardware that has external
memory controllers.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>