rockchip: Enable bootstage on rockpro64

rockchip: Enable bootstage on rockpro64

This board is useful for benchmarking overall U-Boot performance. Enable
the bootstage feature so we get a report.

Since this returns to the boot rom before finishing executing
board_init_r() in SPL, add a few bootstage calls so that we can collect
timing from TPL.

For the stash region, use a portion of SRAM, 64KB below the stack top.
This allows the TPL image to be up to nearly 120KB (it is typically about
64KB). SPL normally runs from SDRAM at 0, so can use the same stash
region.

Signed-off-by: Simon Glass <sjg@chromium.org>