tools/kvm_stat: Fix kvm_exit filter name

tools/kvm_stat: Fix kvm_exit filter name

The filter name is fixed to "exit_reason" for some kvm_exit events, no
matter what architect we have. Actually, the filter name ("exit_reason")
is only applicable to x86, meaning it's broken on other architects
including aarch64.

This fixes the issue by providing various kvm_exit filter names, depending
on architect we're on. Afterwards, the variable filter name is picked and
applied through ioctl(fd, SET_FILTER).

Reported-by: Andrew Jones <[email protected]>
Signed-off-by: Gavin Shan <[email protected]>
Cc: [email protected]
Signed-off-by: Paolo Bonzini <[email protected]>