powerpc/qe: Make qe_reset() code path safe for repeated invocation

For MPC8569 CPUs we'll need to reset QE after each suspend, so make
qe_reset() code path suitable for repeated invocation, that is:

- Don't initialize rheap structures if already initialized;
- Don't allocate muram for SDMA if already allocated, just reinitialize
  registers with previously allocated muram offset;
- Remove __init attributes from qe_reset() and cpm_muram_init();

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>