xen: build fix GNU sed vs. BSD sed

xen: build fix GNU sed vs. BSD sed

Fixes the build error below:

gmake[5]: Entering directory `xen/arch/x86/boot'
gcc  -O1 -fno-omit-frame-pointer -fno-optimize-sibling-calls -m32
-march=3Di686 -g -fno-strict-aliasing -std=3Dgnu99 -Wall
-Wstrict-prototypes
-Wno-unused-value -Wdeclaration-after-statement  -fno-stack-protector
-Werror -fno-builtin -msoft-float -c reloc.c -o reloc.o
ld -melf_i386 -N -Ttext  -o reloc.lnk reloc.o
ld: invalid hex number `-o'

BSD sed does not support the '+' in the basic re while gnu sed does.
BSD sed supports '+' in the extended re and uses the -E flag while
gnu sed uses -r.

The only difference with the original version is that the '+'
qualifier is replaced with '\{1\,\}' which should work with both BSD
sed and GNU sed.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>