common: Fix cpu nr type which is always unsigned type

cpu_cmd() is reading cpu number via simple_strtoul() which is always
unsigned type.
Platform code implementations are not expecting that nr can be negative
and there is not checking in the code for that too.

This patch is using u32 type for cpu number to make sure that platform
code get proper value range.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/arm/mach-imx/mx6/mp.c b/arch/arm/mach-imx/mx6/mp.c
index c3806dc..eda168d 100644
--- a/arch/arm/mach-imx/mx6/mp.c
+++ b/arch/arm/mach-imx/mx6/mp.c
@@ -29,20 +29,20 @@
 	SRC_SCR_CORE_3_ENABLE_MASK
 };
 
-int cpu_reset(int nr)
+int cpu_reset(u32 nr)
 {
 	/* Software reset of the CPU N */
 	src->scr |= cpu_reset_mask[nr];
 	return 0;
 }
 
-int cpu_status(int nr)
+int cpu_status(u32 nr)
 {
 	printf("core %d => %d\n", nr, !!(src->scr & cpu_ctrl_mask[nr]));
 	return 0;
 }
 
-int cpu_release(int nr, int argc, char *const argv[])
+int cpu_release(u32 nr, int argc, char *const argv[])
 {
 	uint32_t boot_addr;
 
@@ -78,7 +78,7 @@
 	return 1;
 }
 
-int cpu_disable(int nr)
+int cpu_disable(u32 nr)
 {
 	/* Disable the CPU N */
 	src->scr &= ~cpu_ctrl_mask[nr];