xen/arm: vpsci: Remove parameter 'ver' from do_common_cpu

xen/arm: vpsci: Remove parameter 'ver' from do_common_cpu

Currently, the behavior of do_common_cpu will slightly change depending
on the PSCI version passed in parameter. Looking at the code, more the
specific 0.2 behavior could move out of the function or adapted for 0.1:

    - x0/r0 can be updated on PSCI 0.1 because general purpose registers
    are undefined upon CPU on. This was deduced from the spec not
    mentioning the state of general purpose registers on CPU on.
    - PSCI 0.1 does not defined PSCI_ALREADY_ON. However, it would be
    safer to bail out if the CPU is already on.

Based on this, the parameter 'ver' is removed and do_psci_cpu_on
(implementation for PSCI 0.1) is adapted to avoid returning
PSCI_ALREADY_ON.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Volodymyr Babchuk <volodymyr.babchuk@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>