pxa: Add weak attribute to reset_cpu() function

This commit allows pxa2xx based boards to reimplement reset_cpu()
function with board specific reset sequence.

Signed-off-by: Lukasz Dalek <luk0104@gmail.com>

arch/arm/cpu/pxa/pxa2xx.c

@@ -284,7 +284,7 @@ void i2c_clk_enable(void)
 	writel(readl(CKEN) | CKEN14_I2C, CKEN);
 }
 
-void reset_cpu(ulong ignored) __attribute__((noreturn));
+void __attribute__((weak)) reset_cpu(ulong ignored) __attribute__((noreturn));
 
 void reset_cpu(ulong ignored)
 {