soc: qcom: smem: Add qcom_smem_is_available()

Avoid having to look up a dummy item from SMEM to detect if it is
already available or if we need to defer probing.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://lore.kernel.org/r/20230531-rpm-rproc-v3-7-a07dcdefd918@gerhold.net
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

include/linux/soc/qcom/smem.h

@@ -4,6 +4,7 @@
 
 #define QCOM_SMEM_HOST_ANY -1
 
+bool qcom_smem_is_available(void);
 int qcom_smem_alloc(unsigned host, unsigned item, size_t size);
 void *qcom_smem_get(unsigned host, unsigned item, size_t *size);