openocd: remove BR2_ARCH_HAS_ATOMICS dependency

For some reason, since when openocd was introduced, it was using a
BR2_ARCH_HAS_ATOMICS dependency for all sub-options that selected
BR2_PACKAGE_LIBFTDI1, even if the libftdi1 package did not have any
atomics dependency. Maybe it was confused with the libftdi package,
which did have a BR2_ARCH_HAS_ATOMICS dependency ?

Regardless, openocd with all four sub-options that currently depend on
BR2_ARCH_HAS_ATOMICS builds perfectly fine with a toolchain that does
not implement any of the __sync atomic built-ins, so we can remove the
BR2_ARCH_HAS_ATOMICS dependency.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>