hwspinlock: sprd: Switch to SPDX license identifier

Use the appropriate SPDX license identifiers in the Spreadtrum hardware
spinlock driver source file and drop the previous boilerplate license text.

Cc: Baolin Wang <baolin.wang@spreadtrum.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>