docs: proc: update VmFlags documentation in smaps

Remove outdated VM_DENYWRITE("dw") reference and add missing
VM_LOCKONFAULT("lf") and VM_UFFD_MINOR("ui") flags.

[akpm@linux-foundation.org: add "dp" (VM_DROPPABLE), per Tal]
Link: https://lkml.kernel.org/r/20250607153614.81914-1-wangfushuai@baidu.com


Signed-off-by: wangfushuai <wangfushuai@baidu.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Mariano Pache <npache@redhat.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Tal Zussman <tz2294@columbia.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>