serial: msm_geni_serial: Use only watermark interrupt instead stale

In some scenario it's observed that there is no stale
event interrupt getting generated, hence use only
watermark interrupt and accordingly change packaging
configuration.

Change-Id: Id15b5222688f8dd5543bd7f67e2c61add8134bd5
Signed-off-by: Prudhvi Yarlagadda <pyarlaga@codeaurora.org>