powerpc: dts: p2020: Do not automatically disable spi@7000 node in p2020-post.dtsi

powerpc: dts: p2020: Do not automatically disable spi@7000 node in p2020-post.dtsi

Device tree include file p2020-post.dtsi should be included after the board
device tree file and overrides settings of the board. So it should not
disable some node as board cannot enable it via normal way (it has to
enable it after inclusion of p2020-post.dtsi file).

Fix it by removal of explicit disable in p2020-post.dtsi file and then
remove explicit post-post enable in all P2020 board device tree files.
Currently no P2020 board has spi@7000 node disabled.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>