x86: detangle meraki-mx100 / nu801 build confusion

x86: detangle meraki-mx100 / nu801 build confusion

Grommish reported the dreaded build error that happend with 5.4
since the kernel didn't have the cgpio v2 interface. His reason
for the removed 5.4 was that the octeon target had a memory leak
issue, so he had to backport the removed 5.4 kernel for his tests.

Chen Minqiang chimed in and noted that no matter what (i.e.
@TARGET_x86 in depends) didn't prevent the package from being build
on other targets.

From what I can tell, the reason for this was that +nu801 meant
that kmod-meraki-mx100 pulled in an unconditional dependency as
part of to the kernel build.

|scripts/package-metadata.pl mk tmp/.packageinfo
|
|$(curdir)/kernel/linux/compile += $(curdir)/firmware/linux-firmware/compile \
|	$(curdir)/firmware/prism54-firmware/compile \
|	$(curdir)/kernel/gpio-button-hotplug/compile \
|	>>> $(curdir)/system/gpio-cdev/nu801/compile <<<

change this by making the dependency conditional on the
meraki-mx100 module itself. Note that the nu801 enables/sets
the  KCONFIG for the cgpio v2 interface itself, since the
userspace program and not the kernel meraki-mx100 relies on it.

Reference: <https://github.com/openwrt/openwrt/commit/eeb8fd4ce7e9>
Reported-by: Grommish <grommish@gmail.com>
Reported-by: Chen Minqiang <ptpt52@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>