powerpc: mpc85xx: Rename _start_e500 symbol to _start

The real entry point is _start_e500. There is no _start symbol at all. So
rename _start_e500 to _start for convension that _start symbol is used as
entry point.

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