omap: Serial: Define register access modes in LCR

Access to some registers depends on register access mode
Three different modes are available for OMAP (at least)
• Operational mode     LCR_REG[7] = 0x0
• Configuration mode A LCR_REG[7] = 0x1 and LCR_REG[7:0]! = 0xBF
• Configuration mode B LCR_REG[7] = 0x1 and LCR_REG[7:0]  = 0xBF

Define access modes and remove redefinitions and magic numbers
in serial drivers (and later in bluetooth driver).

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
Acked-by: Govindraj.R <govindraj.raja@ti.com>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>