hwspinlock/u8500: Switch to SPDX license identifier

Use the appropriate SPDX license identifier in the U8500 HWSEM
driver source file and drop the previous boilerplate license text.

Cc: Mathieu J. Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>