atsam: sysio support is only available on sam4s

Fix sam4e build error introduced in commit f723a314.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/atsam/gpio.c

@@ -60,6 +60,8 @@ set_pull_up(Pio *regs, uint32_t bit, int32_t pull_up)
         regs->PIO_PUDR = bit;
         regs->PIO_PPDDR = bit;
     }
+#endif
+#if CONFIG_MACH_SAM4S
     // Check if this pin is a "system IO pin" and disable if so
     if (regs == PIOB && (bit & 0x1cf0))
         MATRIX->CCFG_SYSIO |= bit;