mm, page_alloc: put should_fail_alloc_page() back behing CONFIG_FAIL_PAGE_ALLOC

This mostly reverts commit af3b8544

 ("mm/page_alloc.c: allow error
injection").  The commit made should_fail_alloc_page() a noinline function
that's always called from the page allocation hotpath, even if it's empty
because CONFIG_FAIL_PAGE_ALLOC is not enabled, and there is no option to
disable it and prevent the associated function call overhead.

As with the preceding patch "mm, slab: put should_failslab back behind
CONFIG_SHOULD_FAILSLAB" and for the same reasons, put the
should_fail_alloc_page() back behind the config option.  When enabled, the
ALLOW_ERROR_INJECTION and BTF_ID records are preserved so it's not a
complete revert.

Link: https://lkml.kernel.org/r/20240711-b4-fault-injection-reverts-v1-2-9e2651945d68@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Christoph Lameter <cl@lin...