power: smb5: Enable updating of RECHARGE_SOC PSY property

Currently, reading the POWER_SUPPLY_PROP_RECHARGE_SOC property returns
a static, cached value initially set to the threshold value specified in
the device tree. Update this cached value whenever the threshold value
is successfully written to.

Also, move the setting of the threshold value to a separate function.

CRs-Fixed: 2249337
Change-Id: I2a476f59cde21540ee10d0623724105df7933b14
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>