arm/css/scpi: Don't panic if the SCP fails to respond

Instead, pass back the error to the calling function. This allows
platform code to fall back to another PSCI implementation if
scpi_wait_ready() or a later SCPI command fails.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Change-Id: Ib4411e63c2512857f09ffffe1c405358dddeb4a6
1 file changed