[MIPS] Drop unneeded config options for RBTX4938

Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -558,9 +558,7 @@ config TOSHIBA_RBTX4927
 
 config TOSHIBA_RBTX4938
 	bool "Toshiba RBTX4938 board"
-	select HAVE_STD_PC_SERIAL_PORT
 	select DMA_NONCOHERENT
-	select GENERIC_ISA_DMA
 	select HAS_TXX9_SERIAL
 	select HW_HAS_PCI
 	select IRQ_CPU