floss: Add a sysprop for initiating PHYs in LE create ext connection

Some ChromeOS devices like sarien couldn't create LE connection with
BLE mice while specifying more than one initiating PHYs in
the LE Extended Create Connection command.
This patch adds a sysprop for Floss to create LE connection with only
LE 1M PHY when needed.  By default, it allows 2M and coded PHYs if the
underlying BT controllers supports them and thus won't affect current
settings of LE Extended Connection for Android devices.

Bug: 260677740
Tag: #floss
Test: Manual test - pairing with BLE mouse
Change-Id: I15d98c2d40e50303e1024f2b8c08980ba67cc421