powerpc: mpc85xx: Drop _start symbol

powerpc: mpc85xx: Drop _start symbol

_start symbol contains only 32-bit data number 0x27051956 despite it is
marked as text section. This magic number is IH_MAGIC which is used for
marking uboot image header.

mpc85xx start.S code does not define valid uboot image header, so IH_MAGIC
number in _start symbol is useless there.

Moreover this _start symbol is not used at all. Entry point is at symbol
_start_e500.

So because this _start symbol is not used for anything, completely remove
it with IH_MAGIC number. After _start symbol was _start_cont symbol, so
replace all relative address calculations by _start_cont.

Signed-off-by: Pali Rohár <pali@kernel.org>
[Rebased]
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>