ARM: kirkwood: Remove redundant kexec code

The PCIe driver has been fully clock aware for quite a while.  Remove
the kexec code to enable the PCIe clock, since the PCIe driver will do
the right thing.

jac adds:
  [arnd]: fixes a build error when KEXEC is enabled and KIRKWOOD_LEGACY is not

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>