at91sam9/at91cap: improve clock framework

calculate dynamically the clock rate and pllb setting for usb

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/include/asm-arm/arch-at91/hardware.h b/include/asm-arm/arch-at91/hardware.h
index 4f0e1a7..6b46a36 100644
--- a/include/asm-arm/arch-at91/hardware.h
+++ b/include/asm-arm/arch-at91/hardware.h
@@ -48,4 +48,7 @@
 #error "Unsupported AT91 processor"
 #endif
 
+/* Clocks */
+#define AT91_SLOW_CLOCK		32768		/* slow clock */
+
 #endif