powerpc/85xx: p2020: Define just one machine description

Combine machine descriptions and code of all P2020 boards into just one
generic unified P2020 machine description. This allows kernel to boot on
any P2020-based board with P2020 DTS file without need to patch kernel and
define a new machine description in 85xx powerpc platform directory.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408140122.25293-12-pali@kernel.org

powerpc/85xx: p2020: Unify .setup_arch and .init_IRQ callbacks

Make just one .setup_arch and one .init_IRQ callback implementation for all
P2020 board code. This deduplicate repeated and same code.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408140122.25293-11-pali@kernel.org

powerpc/85xx: p2020: Move all P2020 RDB machine descriptions to p2020.c

This moves P2020 RDB machine descriptions into new p2020.c source file.
This is preparation for code de-duplication and providing one unified
machine description for all P2020 boards.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408140122.25293-9-pali@kernel.org

powerpc/85xx: p2020: Move all P2020 DS machine descriptions to p2020.c

This moves P2020 DS machine descriptions into new p2020.c source file.
This is preparation for code de-duplication and providing one unified
machine description for all P2020 boards.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230408140122.25293-8-pali@kernel.org