public: add and enable XENFEAT_ARM_SMCCC_supported feature

public: add and enable XENFEAT_ARM_SMCCC_supported feature

This feature indicates that hypervisor is compatible with ARM
SMC calling convention. Previously hypervisor would inject an
undefined instruction exception if an invalid SMC function were
called or would crash a domain if an invalid HVC function
were invoked.
XENFEAT_ARM_SMCCC_supported feature means that it safe to invoke
SMC/HVC calls that are compatible with SMC calling convention.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>