platform: qpnp-revid: add support to identify PMI8940

PMI8940 has same subtype as PMI8950 and is identified by
SPARE0, add support to detect PMI8940.
Add the name 'PMI8940' to the list of pmic names.

CRs-Fixed: 1011021
Change-Id: Ia642c48fe85c18091c14b2a28a9b0fee847227cd
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>