ARM: psci: boot_secondary: replace __pa with virt_to_idmap

On some PAE systems (e.g. TI Keystone), memory is above the 32-bit
addressable limit, and the interconnect provides an aliased view of
parts of physical memory in the 32-bit addressable space. This alias
is strictly for boot time usage, and is not otherwise usable because
of coherency limitations.

In this case, virt_to_phys(secondary_startup) would return the
physical address of the secondary CPU boot entry point, but on such
systems, this would be above the 4GB limit.

A separate function, virt_to_idmap(), has been provided to return a
usable physical address for functions in the identity mapping, and
this must be used in preference to virt_to_phys() or __pa() to find
the physical entry point for functions in the identity mapping range.

For other systems, virt_to_idmap() and virt_to_phys() return identical
physical addresses.

Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Tested-by Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
[Mark: apply rmk's suggested rewording]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Will Deacon <will.deacon@arm.com>