nxp: warm reset support to retain ddr content

NXP: Added warm reset handler to handle SMC PSCI_SYSTEM_RESET2
raised from kernel (> 5.4).

As part of first cold boot, DDR training data is stored in N

nxp: warm reset support to retain ddr content

NXP: Added warm reset handler to handle SMC PSCI_SYSTEM_RESET2
raised from kernel (> 5.4).

As part of first cold boot, DDR training data is stored in NV storage.

As part of this SMC handling, following things are done:
- DDR is put in self-refresh mode to retain the content of DDR.
- Reset cause is saved.
- Reset is triggered.

On next boot to last warm-reset, DDR training is restored from
the NV storage.

Signed-off-by: Ashish Kumar <ashish.kumar@nxp.com>
Signed-off-by: Kuldeep Singh <kuldeep.singh@nxp.com>
Signed-off-by: Udit Agarwal <udit.agarwal@nxp.com>
Signed-off-by: Priyanka Singh <priyanka.singh@nxp.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Change-Id: I8e4fb0824887af49e959c93825e2ab0ba887fc9d

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