soc: qcom: glink_smem_native_xprt: Use upper/lower bits helper macros

The helper macros upper_32_bits() and lower_32_bits() exist for splitting
64-bit values into 32-bit values.  Use the macros instead of doing the
casting manually.

Change-Id: If19b9a69c9328986e53c426dd09df659d650d336
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>