mcux: nxp_kinetis: Move HAS_FTM config to ext

SoCs outside the Kinetis family can have the FTM module, so move the
HAS_FTM config from arch/arm/soc/nxp_kinetis to ext/hal/nxp/mcux

Note that 'select HAS_FTM' was previously missing from Kconfig.soc and
is now fixed.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>