spi: dw-bt1: Fix undefined devm_mux_control_get symbol

I mistakenly added the select attributes to the SPI_DW_BT1_DIRMAP config
instead of having them defined in SPI_DW_BT1. If the kernel doesn't have
the MULTIPLEXER and MUX_MMIO configs manually enabled and the
SPI_DW_BT1_DIRMAP config hasn't been selected, Baikal-T1 SPI device will
always fail to be probed by the driver. Fix that and the error reported by
the test robot:

>> ld.lld: error: undefined symbol: devm_mux_control_get
   >>> referenced by spi-dw-bt1.c
   >>> spi/spi-dw-bt1.o:(dw_spi_bt1_sys_init) in archive drivers/built-in.a

by moving the MULTIPLEXER/MUX_MMIO configs selection to the SPI_DW_BT1
config.

Link: https://lore.kernel.org/lkml/202011161745.uYRlekse-lkp@intel.com/
Link: https://lore.kernel.org/linux-spi/20201116040721.8001-1-rdunlap@infradead.org/
Fixes: abf00907 ("spi: dw: Add Baikal-T1 SPI Controller glue driver")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20201127144612.4204-1-Sergey.Semin@baikalelectronics.ruSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/Kconfig

@@ -255,6 +255,8 @@ config SPI_DW_MMIO
 config SPI_DW_BT1
 	tristate "Baikal-T1 SPI driver for DW SPI core"
 	depends on MIPS_BAIKAL_T1 || COMPILE_TEST
+	select MULTIPLEXER
+	select MUX_MMIO
 	help
 	  Baikal-T1 SoC is equipped with three DW APB SSI-based MMIO SPI
 	  controllers. Two of them are pretty much normal: with IRQ, DMA,
@@ -268,8 +270,6 @@ config SPI_DW_BT1
 config SPI_DW_BT1_DIRMAP
 	bool "Directly mapped Baikal-T1 Boot SPI flash support"
 	depends on SPI_DW_BT1
-	select MULTIPLEXER
-	select MUX_MMIO
 	help
 	  Directly mapped SPI flash memory is an interface specific to the
 	  Baikal-T1 System Boot Controller. It is a 16MB MMIO region, which