soc: arm: atmel: sam4s: Setup external crystal only once

If the SoC uses an external main clock it should not be set both
in the bootloader and the application.

Skip if the internal RC oscillator is disabled.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

soc/arm/atmel_sam/sam4s/soc.c

@@ -43,6 +43,11 @@ static ALWAYS_INLINE void clock_init(void)
 #endif /* CONFIG_SOC_ATMEL_SAM4S_EXT_SLCK */
 
 #ifdef CONFIG_SOC_ATMEL_SAM4S_EXT_MAINCK
+	/* Skip if the internal oscillator is already disabled (for example in a bootloader) */
+	if (!(PMC->PMC_SR & PMC_SR_MOSCRCS)) {
+		goto osc_end;
+	}
+
 	/*
 	 * Setup main external crystal oscillator.
 	 */
@@ -120,6 +125,8 @@ static ALWAYS_INLINE void clock_init(void)
 	}
 #endif /* CONFIG_SOC_ATMEL_SAM4S_EXT_MAINCK */
 
+osc_end:
+
 	/*
 	 * Setup PLLA
 	 */