x86/boot: Rationalise .gitignore

Strip all related content out of the root .gitignore, and provide a
more local .gitignore's with up-to-date patterns.

Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

.gitignore

@@ -212,9 +212,6 @@ xen/.config
 xen/.config.old
 xen/.xen.elf32
 xen/System.map
-xen/arch/x86/boot/mkelf32
-xen/arch/x86/boot/*.bin
-xen/arch/x86/boot/*.lnk
 xen/arch/x86/efi.lds
 xen/arch/x86/efi/check.efi
 xen/arch/x86/efi/mkreloc

xen/arch/x86/boot/.gitignore

@@ -0,0 +1,3 @@
+/mkelf32
+/*.bin
+/*.lnk