target/loongarch: Define function loongarch_cpu_post_init as static

target/loongarch: Define function loongarch_cpu_post_init as static

Function loongarch_cpu_post_init() is implemented and used in the
same file target/loongarch/cpu.c, it can be defined as static function.

This patch moves implementation about function loongarch_cpu_post_init()
before it is referenced. And it is only code movement, no function
change.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>