u-boot.elf: remove hard-coded arm64 flags

This is needed in order to allow building it for other archs.
Move relocation comment to a better place.
Remove no longer needed dts FIXME.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index 2143633..a5eebb9 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -30,6 +30,12 @@
 
 PLATFORM_CPPFLAGS += -D__ARM__
 
+ifdef CONFIG_ARM64
+PLATFORM_ELFFLAGS += -B aarch64 -O elf64-littleaarch64
+else
+PLATFORM_ELFFLAGS += -B arm -O elf32-littlearm
+endif
+
 # Choose between ARM/Thumb instruction sets
 ifeq ($(CONFIG_$(SPL_)SYS_THUMB_BUILD),y)
 AFLAGS_IMPLICIT_IT	:= $(call as-option,-Wa$(comma)-mimplicit-it=always)