x86, doc: Clarify the use of asm("%edx") in uaccess.h
x86, doc: Clarify the use of asm("%edx") in uaccess.h

Put in a comment that explains that the use of asm("%edx") in
uaccess.h doesn't actually necessarily mean %edx alone.

Cc: Jamie Lokier <b4dde37aa2aac745c0e6c43447507eaeace3e59f@shareable.org>
Cc: Ville Syrjälä <cd6e8d405ca90be3a03d5427c5b24fbd2d68dcc4@linux.intel.com>
Cc: Borislav Petkov <0691a664b24b6f15b20cd5aee64b72271db08be1@alien8.de>
Cc: Russell King <ba324ca7b1c77fc20bb970d5aff6eea9377918a5@arm.linux.org.uk>
Cc: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Cc: H. J. Lu <e6b730070cb8ff71eb70dcaf29e26324d883b33b@gmail.com>
Link: ce55f41b6c48c5967e8b8c0b81892bcde4e5921e@zytor.com
Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@linux.intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas