include: configs: brppt1: Fix commit 0ea4fc4d

Commit 0ea4fc4d ("board/BuR: invalidate ${dtbaddr} before cfgscr")
destroys the boot targets b_t30lgcy#0 and b_t30lgcy#1. The reason behind
this is, that b_t30lgcy#0 and b_t30lgcy#1 both load the for booting
needed device trees from mmc and the cfgscr script patches those. Because
of this, cfgscr is not allowed to destroy the previously loaded device
tree otherwise cfgscr will fail.
This patch moves the device trees invalidation on warm restart to the
PREBOOT cmd to fix that issue.

Fixes: 0ea4fc4d ("board/BuR: invalidate ${dtbaddr} before cfgscr")
Signed-off-by: Bernhard Messerklinger <bernhard.messerklinger@br-automation.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>