lguest: rename switcher_page to switcher_pages.

There is a single page with the Switcher in it, but it's followed by 2
pages per Host CPU.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --cc drivers/lguest/core.c
Simple merge

diff --cc drivers/lguest/lg.h
Simple merge

diff --cc drivers/lguest/page_tables.c
Simple merge