ACPI / OF: Rename of_node() and acpi_node() to to_of_node() and to_acpi_node()

Commit 8a0662d9 introduced of_node and acpi_node symbols in global namespace
but there were already ~63 of_node local variables or function parameters
(no single acpi_node though, but anyway).

After debugging undefined but used of_node local varible (which turned out
to reference static function of_node() instead) it became clear that the names
for the functions are too short and too generic for global scope.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>