board: atmel: clean up peripheral clock code

Due to introducing the new peripheral clock handle functions,
use these functions to reduce duplicated code.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Tested-by: Heiko Schocher <hs@denx.de>
[Rebased on current master, fixup for at91rm9200ek]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/board/siemens/smartweb/smartweb.c b/board/siemens/smartweb/smartweb.c
index d82f1b7..e7ee65c 100644
--- a/board/siemens/smartweb/smartweb.c
+++ b/board/siemens/smartweb/smartweb.c
@@ -22,7 +22,6 @@
 #include <asm/arch/at91sam9260_matrix.h>
 #include <asm/arch/at91sam9_smc.h>
 #include <asm/arch/at91_common.h>
-#include <asm/arch/at91_pmc.h>
 #include <asm/arch/at91_spi.h>
 #include <spi.h>
 #include <asm/arch/clk.h>
@@ -126,7 +125,7 @@
 	/* Enable UDPCK clock, MCK is enabled in at91_clock_init() */
 	at91_periph_clk_enable(ATMEL_ID_UDP);
 
-	writel(AT91SAM926x_PMC_UDP, &pmc->scer);
+	at91_system_clk_enable(AT91SAM926x_PMC_UDP);
 }
 
 struct at91_udc_data board_udc_data  = {