arm/lpc32xx/include/bsp/lpc32xx.h: Add unused element in structure

This header file defines multiple empty structures which are
reported as errors by the test spstdc17 using GCC 15.  Added an element
named "unused" to each structure. The macro LPC32XX_FILL() was
checked to ensure it handles the modified structure correctly.

Closes #5295.

bsps/arm/lpc32xx/include/bsp/lpc32xx.h

@@ -238,39 +238,51 @@
 #define LPC32XX_RESERVE(a, b) uint8_t reserved_ ## b [b - a]
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_nand_slc;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_ssp;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_spi;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_sd_card;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_usb;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_lcd;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_etb;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_syscon;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_uart_ctrl;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_uart;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_ms_timer;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_hs_timer;
 
 /**
@@ -345,18 +357,23 @@ typedef struct {
 } lpc32xx_wdt;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_debug;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_adc;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_keyscan;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_pwm;
 
 typedef struct {
+  uint32_t unused;
 } lpc32xx_mcpwm;
 
 typedef struct {