uchcom: remove UCHCOM_REG_BREAK2 alias of UCHCOM_REG_LCR1

Also, add definitions for more bits of UCHCOM_REG_LCR1 as seen in the
Linux driver. UCHCOM_LCR1_PARENB definition was different from that in
the Linux driver and clashed with newly added UCHCOM_LCR1_RX. I took a
liberty to change UCHCOM_LCR1_PARENB to the Linux definition as it was
unused in the driver anyway. This change should make
uchcom_cfg_set_break() easier to understand.

Approved by: hselasky
MFC after: 2 weeks