slippy: Add iSSD power sequencing

Without an LM10506-A the power sequencing for this
part needs to be done manually using GPIOs.

Change-Id: I842152e5f7c30c8dbe37df0c344935a659eb2887
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/49648
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/4150
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
1 file changed