firmware: imx: Add stub functions for SCMI CPU API

To ensure successful builds when CONFIG_IMX_SCMI_CPU_DRV is not enabled,
this patch adds static inline stub implementations for the following
functions:

  - scmi_imx_cpu_start()
  - scmi_imx_cpu_started()
  - scmi_imx_cpu_reset_vector_set()

These stubs return -EOPNOTSUPP to indicate that the functionality is not
supported in the current configuration. This avoids potential build or
link errors in code that conditionally calls these functions based on
feature availability.

Fixes: 1055faa ("firmware: imx: Add i.MX95 SCMI CPU driver")
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Author: MrVan

include/linux/firmware/imx/sm.h

@@ -41,10 +41,28 @@ static inline int scmi_imx_misc_ctrl_set(u32 id, u32 val)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_IMX_SCMI_CPU_DRV)
 int scmi_imx_cpu_start(u32 cpuid, bool start);
 int scmi_imx_cpu_started(u32 cpuid, bool *started);
 int scmi_imx_cpu_reset_vector_set(u32 cpuid, u64 vector, bool start, bool boot,
 				  bool resume);
+#else
+static inline int scmi_imx_cpu_start(u32 cpuid, bool start)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int scmi_imx_cpu_started(u32 cpuid, bool *started)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int scmi_imx_cpu_reset_vector_set(u32 cpuid, u64 vector, bool start,
+						bool boot, bool resume)
+{
+	return -EOPNOTSUPP;
+}
+#endif
 
 enum scmi_imx_lmm_op {
 	SCMI_IMX_LMM_BOOT,