ipc: send generic reply for pm_context messages

[tlauda]

Uses generic reply for pm_context ipc messages.

Signed-off-by: Tomasz Lauda tomasz.lauda@linux.intel.com

[jajanusz]

We need this to properly handle pm ipc responses in tests/driver. I guess there is going to be more data in reply after error code when functionality will be implemented, but for now it looks ok.

[xiulipan]

@tlauda@jajanusz
Will cause regression with linux kernel.
We will check reply size for the IPC.
[ 7.288822] sof-audio sof-audio: ipc tx: 0x40010000: GLB_PM_MSG: CTX_SAVE
[ 7.288895] sof-audio sof-audio: error: reply expected 0x40 got 0xc bytes
[ 7.288935] sof-audio sof-audio: error: ipc error for 0x40010000 size 0x40
[ 7.288941] sof-audio sof-audio: error: ctx_save ipc error during suspend -22
[ 7.288953] sof-audio-pci 0000:00:0e.0: can't suspend (snd_sof_runtime_suspend [snd_sof] returned -22)

[lgirdwood]

@tlauda will the PM context be deprecated now or will it be modified in the future ? My thinking here is that we can remove the structure from the IPC definition if it will never be used atm ?