powerpc/pseries: add definitions for new H_SIGNAL_SYS_RESET hcall

This has not made its way to a PAPR release yet, but we have an hcall
number assigned.

  H_SIGNAL_SYS_RESET = 0x380

  Syntax:
    hcall(uint64 H_SIGNAL_SYS_RESET, int64 target);

  Generate a system reset NMI on the threads indicated by target.

  Values for target:
    -1 = target all online threads including the caller
    -2 = target all online threads except for the caller
    All other negative values: reserved
    Positive values: The thread to be targeted, obtained from the value
    of the "ibm,ppc-interrupt-server#s" property of the CPU in the OF
    device tree.

  Semantics:
  - Invalid target: return H_Parameter.
  - Otherwise: Generate a system reset NMI on target thread(s),
    return H_Success.

This will be used by crash/debug code to get stuck CPUs into a known
state.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>