powerpc: Update MPC5XXX MAINTAINERS entry

It's several years since the last commit from Anatolij, so mark
MPC5XXX as "Odd Fixes" rather than "Maintained".

Also the git link no longer works so remove it.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Anatolij Gustschin <agust@denx.de>
Link: https://lore.kernel.org/r/20200224233146.23734-6-mpe@ellerman.id.au