soc/arm/silabs_exx32: clean up use of extern "C"

Remove extern "C" support from files that don't declare symbols subject
to language linkage effects.

Consistently place C++ use of extern "C" after all include directives,
within the negative branch of _ASMLANGUAGE if used.

Background from issue #17997:

Declarations that use C linkage should be placed within extern "C"
so the language linkage is correct when the header is included by
a C++ compiler.

Similarly #include directives should be outside the extern "C" to
ensure the language-specific default linkage is applied to any
declarations provided by the included header.

See: https://en.cppreference.com/w/cpp/language/language_linkage
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

soc/arm/silabs_exx32/common/soc_gpio.h

@@ -14,6 +14,10 @@
 #include <soc.h>
 #include <em_gpio.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct soc_gpio_pin {
 	GPIO_Port_TypeDef port; /** GPIO port */
 	unsigned int pin;       /** GPIO pin on the port */
@@ -27,4 +31,8 @@ struct soc_gpio_pin {
  */
 void soc_gpio_configure(const struct soc_gpio_pin *pin);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _SILABS_EXX32_SOC_GPIO_H_ */

soc/arm/silabs_exx32/efm32hg/soc.h

@@ -15,10 +15,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <em_common.h>
@@ -29,8 +25,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _SOC__H_ */

soc/arm/silabs_exx32/efm32pg12b/soc.h

@@ -15,10 +15,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <em_bus.h>
@@ -30,8 +26,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _SOC__H_ */

soc/arm/silabs_exx32/efm32wg/soc.h

@@ -15,10 +15,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <em_bus.h>
@@ -30,8 +26,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _SOC__H_ */

soc/arm/silabs_exx32/efr32fg1p/soc.h

@@ -15,10 +15,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <em_bus.h>
@@ -30,8 +26,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _SOC__H_ */

soc/arm/silabs_exx32/efr32mg12p/soc.h

@@ -15,10 +15,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <em_common.h>
@@ -29,8 +25,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _SOC__H_ */