ARM: shmobile: Move shmobile_scu_base from .text to .bss

shmobile_scu_base is being written to, so it doesn't belong in the .text
section. Fix this by moving it from asm .text to C .bss, as it's no
longer used from asm code since commit 4f6da36f ("ARM: shmobile:
Remove old SCU boot code").

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