Makefile: support builtin fpga-{mgr,bridge,region} modules

The GSRD (Golden Software Reference Design) Yocto image for Intel
SoCFPGA is built with CONFIG_FPGA=y by default, which causes an
unresolvable symbol conflict with the fpga-mgr backport module.

Assuming that the kernel version is recent enough not to require any
changes to fpga-{mgr,bridge,region}, do not build these modules when
built into the kernel. This is not complete solution and will result
in unknown failures when the builtin kernel modules are too old, but
it does work with GSRD which currently builds with Linux 6.1 (LTS).

Link: https://github.com/altera-opensource/gsrd-socfpga
Link: https://github.com/altera-opensource/linux-socfpga
Signed-off-by: Peter Colberg <[email protected]>

Makefile

@@ -47,9 +47,15 @@ endif
 # The module order matters; it determines the module order for
 # both the insmod and rmmod targets. The module order is also
 # leveraged for install packages by the dkms.conf file.
+ifneq ($(CONFIG_FPGA),y)
 obj-m += fpga-mgr.o
+endif
+ifneq ($(CONFIG_FPGA_BRIDGE),y)
 obj-m += fpga-bridge.o
+endif
+ifneq ($(CONFIG_FPGA_REGION),y)
 obj-m += fpga-region.o
+endif
 ifndef CONFIG_FW_UPLOAD
 obj-m += fpga-image-load.o
 endif