community/libcec: missing Linux API support

Using an Aarch64 system which exposes CEC support through the Linux CEC API through /dev/cec0 libcec/cec-client seems not to work. It seems that the backend is not enabled, from the latest build logs:

-- Configured features:
-- Pulse-Eight CEC Adapter:                yes
-- Pulse-Eight CEC Adapter detection:      yes
-- xrandr support:                         yes
-- Raspberry Pi support:                   no
-- TDA995x support:                        no
-- Exynos support:                         no
-- DRM support:                            yes
-- Linux support:                          no
-- AOCEC support:                          no
-- i.MX6 support:                          no
-- Python support:                         version 3.10.1 (3.10)
-- lib info: git revision: v3.15.0+3602-6ffc0f6, compiled on 2022-01-03 07:45:02 by buildozer@build-edge-x86.local on Linux 5.15.12-0-lts (i686), features: P8_USB, DRM, P8_detect, randr
-- Configuring done

(Linux support is no).

This should be quite straight forward to resolve by adding -DHAVE_LINUX_API=1 to the cmake invocation.

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