mfd: syscon: Remove unused Exynos PMU headers

Since commit 5812f010 ("phy: exynos4: Remove duplicated defines of
PHY register defines") and commit 7a66647b

 ("phy: exynos: Use one
define for enable bit") all users of syscon Exynos PMU headers (for PHY
drivers) are converted to use different headers so these can be removed.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>