regulator: s2mpa01: Drop initialization via platform data

None of the platforms with S2MPA01 use board files, so any
initialization via platform data can be safely removed.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210420170244.13467-4-krzysztof.kozlowski@canonical.com
Signed-off-by: Mark Brown <broonie@kernel.org>