mips: ralink: remove reset related code

A proper clock driver for ralink SoCs has been added. This driver is also
a reset provider for the SoC. Hence there is no need to have reset related
code in 'arch/mips/ralink' folder anymore. The only code that remains is
the one related with mips_reboot_setup where a PCI reset is performed.
We maintain this because I cannot test old ralink board with PCI to be
sure all works if we remove also this code.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>