MAINTAINERS: Add some information to PARAVIRT_OPS entry

Most patches for paravirt_ops are going through the tip tree, as those
patches tend to touch x86 specific files a lot.

Add the x86 ML and the tip tree to the PARAVIRT_OPS MAINTAINERS entry
in order to reflect that.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20211104095955.4813-1-jgross@suse.com