soc: qcom: Select QMI Helper functions standalone

The QRTR sample may not always be enabled. Allow the QMI Helper
functions to be selected by adding a label and a dependency on QRTR.
Remove the selects statement in the samples Kconfig.

Change-Id: I4c77381bab32f4579ca9aaa05bd76ff569cb3817
Signed-off-by: Chris Lew <clew@codeaurora.org>