ARM: hisi: make unexported symbols static

The two functions hix5hd2_set_scu_boot_addr() and
hip01_set_boot_addr() are not declared or exported
outside arch/arm/mach-hisi/platsmp.c file. Avoid
the following warnings by making them static:

arch/arm/mach-hisi/platsmp.c:142:6: warning: symbol 'hip01_set_boot_addr' was not declared. Should it be static?
arch/arm/mach-hisi/platsmp.c:106:6: warning: symbol 'hix5hd2_set_scu_boot_addr' was not declared. Should it be static?

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>