soc: andestech: refactor out soc_early_init_hook() from pma.c

Refactor out the `soc_early_init_hook()` function from `pma.c` to
`soc.c` which is always compiled so that it can be extended to run
other init functions easily in the future. Then, restore the function
in `pma.c` to `pma_init()`.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>