ARM: at91: move SoC detection to its own driver

To simplify machine init and as the soc_device struct is not used as the
parent for on-chip devices anymore, move SoC detection to its own driver.

Change in dmesg:
 - before:
DMA: preallocated 256 KiB pool for atomic coherent allocations
AT91: Detected SoC family: sama5d2
AT91: Detected SoC: sama5d27, revision 0
No ATAGs?
clocksource: tcb_clksrc: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 184217874325 ns
at_xdmac f0010000.dma-controller: 16 channels, mapped at 0xe085b000
SCSI subsystem initialized

 - after:
DMA: preallocated 256 KiB pool for atomic coherent allocations
No ATAGs?
clocksource: tcb_clksrc: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 184217874325 ns
at_xdmac f0010000.dma-controller: 16 channels, mapped at 0xe0859000
AT91: Detected SoC family: sama5d2
AT91: Detected SoC: sama5d27, revision 0
SCSI subsystem initialized

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
diff --git a/arch/arm/mach-at91/at91rm9200.c b/arch/arm/mach-at91/at91rm9200.c
index d068ec3..656ad40 100644
--- a/arch/arm/mach-at91/at91rm9200.c
+++ b/arch/arm/mach-at91/at91rm9200.c
@@ -14,23 +14,10 @@
 #include <asm/mach/arch.h>
 
 #include "generic.h"
-#include "soc.h"
-
-static const struct at91_soc rm9200_socs[] = {
-	AT91_SOC(AT91RM9200_CIDR_MATCH, 0, "at91rm9200 BGA", "at91rm9200"),
-	{ /* sentinel */ },
-};
 
 static void __init at91rm9200_dt_device_init(void)
 {
-	struct soc_device *soc;
-	struct device *soc_dev = NULL;
-
-	soc = at91_soc_init(rm9200_socs);
-	if (soc != NULL)
-		soc_dev = soc_device_to_device(soc);
-
-	of_platform_default_populate(NULL, NULL, soc_dev);
+	of_platform_default_populate(NULL, NULL, NULL);
 
 	at91rm9200_pm_init();
 }