package/fwts: enable on RISC-V 64-bit
fwts RISC-V 64bit support was introduced in version 20.07.00, see [1].
This commit adds this architecture in _ARCH_SUPPORTS.
[1] https://wiki.ubuntu.com/FirmwareTestSuite/ReleaseNotes/20.07.00
Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>