platform: generic: allwinner: Advertise nonretentive suspend

Add D1's nonretentive suspend state to the devicetree so S-mode software
knows about it and can use it.

Latency and power measurements were taken on an Allwinner Nezha board:
 - Entry latency was measured from the beginning of sbi_ecall_handler()
   to before the call to wfi() in sun20i_d1_hart_suspend().
 - Exit latency was measured from the beginning of sbi_init() to before
   the call to sbi_hart_switch_mode() in init_warmboot().
 - There was a 17.5 mW benefit from non-retentive suspend compared to
   WFI, with a 170 mW cost during the 107 us entry/exit period. This
   provides a break-even point around 1040 us. Residency includes entry
   latency, so round this up to 1100 us.
 - The hardware power sequence latency (after the WFI) is assumed to be
   negligible, so set the wakeup latency to the exit latency.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Samuel Holland <samuel@sholland.org>