arm: traps: handle PSCI calls inside `vsmc.c`

arm: traps: handle PSCI calls inside `vsmc.c`

PSCI is part of HVC/SMC interface, so it should be handled in
appropriate place: `vsmc.c`. This patch moves PSCI handler
calls from `traps.c` to `vsmc.c`. Also it corrects coding
style of the PSCI handler functions.

Older PSCI 0.1 uses SMC function identifiers in range that is
reserved for existing APIs (ARM DEN 0028B, page 16), while newer
PSCI 0.2 and later is defined as "standard secure service" with its
own ranges (ARM DEN 0028B, page 18).

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>