powerpc, mpc83xx: Remove CONFIG_ELBC_BRx_ORx

powerpc, mpc83xx: Remove CONFIG_ELBC_BRx_ORx

Commit 31cb3d770f ("mpc83xx: Migrate CONFIG_SYS_{BR, OR}*_PRELIM to
Kconfig") converted CONFIG_SYS_{BRx/ORx}_PRELIM to Kconfig by
implementing a fine-grained selection of every bit in Kconfig.

But commit 05cda701a7 ("Convert CONFIG_SYS_BR0_PRELIM et al to
Kconfig") reworked it so that you now just have to provide the raw
value of each register in Kconfig. However, all fine-grained
Kconfig items remained allthough they are not used anymore.

Remove them all.

Fixes: 05cda701a7 ("Convert CONFIG_SYS_BR0_PRELIM et al to Kconfig")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>