kexec-tools: Remove duplicated variable declarations

When building kexec-tools for Fedora 32, following error is observed:

/usr/bin/ld: kexec/arch/x86_64/kexec-bzImage64.o:(.bss+0x0): multiple definition of `bzImage_support_efi_boot';
kexec/arch/i386/kexec-bzImage.o:(.bss+0x0): first defined here

/builddir/build/BUILD/kexec-tools-2.0.20/kexec/arch/arm/../../fs2dt.h:33: multiple definition of `my_debug';
kexec/fs2dt.o:/builddir/build/BUILD/kexec-tools-2.0.20/kexec/fs2dt.h:33: first defined here

/builddir/build/BUILD/kexec-tools-2.0.20/kexec/arch/arm64/kexec-arm64.h:68: multiple definition of `arm64_mem';
kexec/fs2dt.o:/builddir/build/BUILD/kexec-tools-2.0.20/././kexec/arch/arm64/kexec-arm64.h:68: first defined here

/builddir/build/BUILD/kexec-tools-2.0.20/kexec/arch/arm64/kexec-arm64.h:54: multiple definition of `initrd_size';
kexec/fs2dt.o:/builddir/build/BUILD/kexec-tools-2.0.20/././kexec/arch/arm64/kexec-arm64.h:54: first defined here

/builddir/build/BUILD/kexec-tools-2.0.20/kexec/arch/arm64/kexec-arm64.h:53: multiple definition of `initrd_base';
kexec/fs2dt.o:/builddir/build/BUILD/kexec-tools-2.0.20/././kexec/arch/arm64/kexec-arm64.h:53: first defined here

And apparently, these variables are wrongly declared multiple times. So
remove duplicated declaration.

Signed-off-by: Kairui Song <kasong@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>