package/fwts: enable for arm

The FWTS application and its associated kernel modules do build on arm;
enable it.

Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>
Cc: Erico Nunes <nunes.erico@gmail.com>
[yann.morin.1998@free.fr: introduce _ARCH_SUPPORTS, sort alphabetically]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>