ARM: at91: Enable SPL_SEPARATE_BSS by default

According to the linker script for both armv7 and arm926ejs based SoC,
BSS section was all the time separated for SPL but this symbol was
only enabled on some boards. However, it is necessary to have it
enabled for OF_SEPARATE configuration where DTB is appended to u-boot
with DTB.

Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 21df1c4..3ba7e33 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -532,6 +532,7 @@
 config ARCH_AT91
 	bool "Atmel AT91"
 	select SPL_BOARD_INIT if SPL && !TARGET_SMARTWEB
+	select SPL_SEPARATE_BSS if SPL
 
 config TARGET_EDB93XX
 	bool "Support edb93xx"