x86, boot: add new generated files to the appropriate .gitignore files

git status complains of untracked (generated) files in arch/x86/boot..

# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#       ../../arch/x86/boot/compressed/mkpiggy
#       ../../arch/x86/boot/compressed/piggy.S
#       ../../arch/x86/boot/compressed/vmlinux.lds
#       ../../arch/x86/boot/voffset.h
#       ../../arch/x86/boot/zoffset.h

..so adjust .gitignore files accordingly.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/boot/.gitignore b/arch/x86/boot/.gitignore
index 172cf8a..851fe93 100644
--- a/arch/x86/boot/.gitignore
+++ b/arch/x86/boot/.gitignore
@@ -3,6 +3,8 @@
 cpustr.h
 mkcpustr
 offsets.h
+voffset.h
+zoffset.h
 setup
 setup.bin
 setup.elf