hwspinlock: u8500_hsem: Remove redundant PM runtime implementation

Since the hwspinlock core has changed the PM runtime to be optional, thus
remove the redundant PM runtime implementation in the u8500 HWSEM driver.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>