ARM: shmobile: r8a7779: Remove remainings of removed SCU boot setup code

Commit 0ca2894b

 ("ARM: shmobile: Use shared SCU SMP boot code on
r8a7779") obsoleted the r8a7779-specific SCU boot code, but forgot to
remove the setup of shmobile_boot_fn and shmobile_boot_arg, which is
overwritten by shmobile_smp_scu_prepare_cpus().

Note that shmobile_scu_base wasn't initialized at that point yet anyway.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>