power: smb2: Fix fake USB insertion from ext_5v_boost

In SDM845, ext_5v_boost can be selected as external source
for boost. When enabled, it raises VBUS and triggers
IRQs just as source insertion. This fake insertion is not
desired.

Identify fake USB insertion and skip IRQs triggered by it.

CRs-Fixed: 2202372
Change-Id: Idfface0f3a66ca9128c2858a9393b296fda7d0f3
Signed-off-by: Harry Yang <harryy@codeaurora.org>