unicore32: modify io_p2v and io_v2p macros, and adjust PKUNITY_mmio_BASEs

1. remove __REG macro
2. add (void __iomem *) to io_p2v macro
3. add (phys_addr_t) to io_v2p macro
4. add PKUNITY_AHB_BASE and PKUNITY_APB_BASE definitions
5. modify all PKUNITY_mmio_BASEs from physical addr to virtual addr
6. adjust prefix macro for all usage of PKUNITY_mmio_BASEs
  -- by advice with Arnd Bergmann

Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>