[PATCH AUTOSEL for 4.9 14/24] serial: 8250: Preserve DLD[7:4] for PORT_XR17V35X

From: Aaron Sierra [ Upstream commit 0ab84da2e076948c49d36197ee7d254125c53eab ] The upper four bits of the XR17V35x fractional divisor register (DLD) control general chip function (RS-485 direction pin polarity, multidrop mode, XON/XOFF parity check, and fast IR mode).

[PATCH AUTOSEL for 4.9 14/24] serial: 8250: Preserve DLD[7:4] for PORT_XR17V35X

From: Aaron Sierra [ Upstream commit 0ab84da2e076948c49d36197ee7d254125c53eab ] The upper four bits of the XR17V35x fractional divisor register (DLD) control general chip function (RS-485 direction pin polarity, multidrop mode, XON/XOFF parity check, and fast IR mode). Don't allow these bits to