of: Split early_init_dt_scan into two parts

of: Split early_init_dt_scan into two parts

Currently, early_init_dt_scan validates the header, sets the
boot params, and scans for chosen/memory all in one function.
Split this up into two separate functions (validation/setting
boot params in one, scanning in another) to allow for
additional setup between boot params and scanning the memory.

Signed-off-by: Laura Abbott <[email protected]>
Tested-by: Andreas Färber <[email protected]>
[glikely: s/early_init_dt_scan_all/early_init_dt_scan_nodes/]
Signed-off-by: Grant Likely <[email protected]>