x86: Fix typos in comments

BIOSen -> BIOSes; paing -> paging. Append to 640 its proper unit "Kb".
encomapssing -> encompassing.

 [ bp: Merge into a single patch, fix one more typo, massage. ]

Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Robert Richter <rrichter@marvell.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20191118070012.27850-1-caoj.fnst@cn.fujitsu.com