x86: provide mb() macro

Implement a x86 memory barrier mb(). Furthermore, remove the previously
used mfence() function, which does the same thing.

The mb() macro is now equivalent to Linux (v6.9):
linux/arch/x86/include/asm/barrier.h

Signed-off-by: Philip Oberfichtner <pro@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
3 files changed