MIPS: Alchemy: remove duplicate UART register offset definitions

MIPS: Alchemy: remove duplicate UART register offset definitions

The UART register names are identical to the ones in uapi/linux/serial_reg.h,
which causes build failures in various drivers when they indirectly pull in
the au1000.h header, for example via gpio.h:

In file included from arch/mips/include/asm/mach-au1x00/gpio.h:13:0,
                 from arch/mips/include/asm/gpio.h:4,
                 from include/linux/gpio.h:48,
                 from include/linux/ssb/ssb.h:9,
                 from drivers/ssb/driver_mipscore.c:11:
arch/mips/include/asm/mach-au1x00/au1000.h:1171:0: note: this is the location of the previous definition
 #define UART_LSR 0x1C /* Line Status Register */

Get rid of the altogether, nothing in the core Alchemy code depends
on them any more.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/6664/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>