x86: rename CONFIG_STACK_SIZE

Configuration variables should have the same meaning independent of the
architecture. x86 and ARM both use CONFIG_STACK_SIZE:

* x86: U-Boot's runtime stack size during reboot
* ARM: max stack size that can be used by U-Boot

Rename the x86 configuration variable to CONFIG_STACK_SIZE_REBOOT

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cbca69e..a34b108 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -811,7 +811,7 @@
 	  graphics console won't work without VGA options ROMs. Set it to N
 	  if your kernel is only on a serial console.
 
-config STACK_SIZE
+config STACK_SIZE_RESUME
 	hex
 	depends on HAVE_ACPI_RESUME
 	default 0x1000