Changes between #523 and #524

lint/checkpatch: fix false FUNCTION_ARGUMENTS

Fix that the linter complains about:
  WARNING:FUNCTION_ARGUMENTS: function definition argument 'void' should also have an identifier name

For functions with attributes at the end, e.g.:
  void Fallback_Handler(void) __attribute__((weak, alias("Dummy_Handler")));

Related: https://gerrit.osmocom.org/c/osmo-ccid-firmware/+/42224/comment/7c5b3be0_6ff61090/
Change-Id: I139bdabb38bd0c9ceda99921ebdc0196850c2a53

lint/checkpatch: support multiple configs

Run checkpatch with any .checkpatch*.conf found in the project dir. This
is in preparation for having two .checkpatch.conf files in osmo-trx, in
order to use different linting rules for C++ code:
* .checkpatch.c.conf
* .checkpatch.c++.conf

Related: osmo-trx I0df5b6f2f0bf1469a80a1f5859809c30f523f683
Change-Id: Ia2e75d9783382cefc3900a4ab51a5a919a2cbbbc