platform/chrome: Don't make CHROME_PLATFORMS depends on X86 || ARM

The Chrome platform support depends on X86 || ARM because there are
only Chromebooks using those architectures. But only some drivers
depend on a given architecture, and the ones that do already have
a dependency on their specific Kconfig symbol entries.

An option is to also make CHROME_PLATFORMS depends on || COMPILE_TEST
but is more future proof to remove the dependency and let the drivers
be built in all architectures if possible to have more build coverage.

Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Lee Jones <lee.jones@linaro.org>