clk: samsung: Use common registration function for pll2550x

There is no such significant differences in pll2550x PLL type
to justify a separate registration function.  This patch adapts
exynos5440 driver to use the common function and removes
samsung_clk_register_pll2550x().

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>