net: rnpgbe: Add n500/n210 chip support with BAR2 mapping

net: rnpgbe: Add n500/n210 chip support with BAR2 mapping

Add hardware initialization foundation for MUCSE 1Gbe controller,
including:
1. Map PCI BAR2 as hardware register base;
2. Bind PCI device to driver private data (struct mucse) and
   initialize hardware context (struct mucse_hw);
3. Reserve board-specific init framework via rnpgbe_init_hw.

Signed-off-by: Dong Yibo <dong100@mucse.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Reviewed-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://patch.msgid.link/20251101013849.120565-3-dong100@mucse.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>