Documentation: x86: Fix obsolete name of page fault handler

Since commit 91eeafea ("x86/entry: Switch page fault exception to
IDTENTRY_RAW"), the function name of the page fault handler is out of date.
And because of commit aa37c51b ("x86/mm: Break out user address space
handling"), the description of search_exception_table is not correct
anymore. It may mislead the user who wants to use the documentation to
figure out the page fault handler.

Also, fix typo and add the parentheses after function and macro name.

Signed-off-by: Chin En Lin <shiyn.lin@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>