powerpc: P2020RDB-PC: Separate from P1_P2_RDB_PC in Kconfig

Use TARGET_P2020RDB_PC instead of sharing with P1_P2_RDB_PC to
simplify Kconfig and config macros.

Remove macro CONFIG_P2020RDB.

Signed-off-by: York Sun <york.sun@nxp.com>
13 files changed