qpnp-revid: move pmi8998 and pm660 FAB_ID definitions to qpnp-revid.h

FAB_ID can be used across multiple drivers that gets revid
information from qpnp-revid driver. Move the FAB_ID definitions
in RR_ADC driver for pmi8998 and pm660 so that they can be
reused by other clients.

Change-Id: Ia61af56244161c948b0f458a77e699c1cac871b1
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>