x86: efi: app: Generate Microsoft PE format compliant image

Per Microsoft PE Format documentation [1], PointerToSymbolTable and
NumberOfSymbols should be zero for an image in the COFF file header.
Currently U-Boot is generating u-boot-app.efi in which these two
members are not zero.

This updates the build rules to tell linker to remove the symbol
table completely so that we can generate compliant *.efi images.

[1] https://docs.microsoft.com/zh-cn/windows/desktop/Debug/pe-formatSigned-off-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: NAlexander Graf <agraf@suse.de>

arch/x86/config.mk

@@ -65,7 +65,7 @@ CPPFLAGS_crt0-efi-$(EFIARCH).o += $(CFLAGS_EFI)
 ifeq ($(CONFIG_EFI_APP),y)
 
 PLATFORM_CPPFLAGS += $(CFLAGS_EFI)
-LDFLAGS_FINAL += -znocombreloc -shared
+LDFLAGS_FINAL += -znocombreloc -shared -s
 LDSCRIPT := $(LDSCRIPT_EFI)
 
 else