realtek: 6.12: adapt platform patch

realtek: 6.12: adapt platform patch

Upstream has integrated the Realtek target into the generic MIPS
initialization and so MACH_REALTEK_RTL has gained some new features.
Especially:

- CONFIG_MACH_GENERIC_CORE generates central modules
- board-realtek module adds device specific extensions

The current downstream initialization works well and upgrading to
kernel 6.12 is not the right time to harmonize this. Modify the
MACH definitions to the current needs.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/18935
Signed-off-by: Robert Marko <robimarko@gmail.com>