use new sdbus++ camelcase for NMI.

Change I17a8d7479556596a3cf252b3f4eae9c8df547189 will change
how sdbus++ generates names which start with an acronym.
Prepare for this by keying off the SDBUSPP_NEW_CAMELCASE
define to use the new format.

Changes:
    nMI() -> nmi()

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I03c7c98cb784da2343719aa7f47b256b1ebcdaff
diff --git a/nmi_interface.hpp b/nmi_interface.hpp
index 9e3f052..d61e8eb 100644
--- a/nmi_interface.hpp
+++ b/nmi_interface.hpp
@@ -33,7 +33,11 @@
 
     /*  @brief trigger stop followed by soft reset.
      */
+#ifdef SDBUSPP_NEW_CAMELCASE
+    void nmi() override;
+#else
     void nMI() override;
+#endif
 
   private:
     /** @brief sdbus handle */