Simplify setting `php-file-patterns` with `mapc`

Rather than a `while` loop, use the functionalerific `mapc` to add file-name
patterns to `auto-mode-alist`.

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Define `php-mode-map` in a `defvar`, as is the recommended style.

See Tips for Defining(elisp).

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>