bios: fix driver binding order

spi-aspeed-smc driver was bound but spi-nor driver was not bound which
created problems for systems with more than one spi device on the bus.

Update the code to bind spi-nor driver as well for the desired device
and not unbind spi-aspeed-smc driver at the end since other spi devices
may still be in use on that bus.

Tested: bios update proceeds normally

Config which was used:

```
    {
      "FirmwareInfo": {
        "CompatibleHardware": "com.tyan.Hardware.S8030.SPI.Host",
        "VendorIANA": 6653
      },
      "MuxOutputs": [
        {
          "Name": "BMC_SPI_SEL",
          "Polarity": "High"
        }
      ],
      "Name": "HostSPIFlash",
      "SPIControllerIndex": 1,
      "SPIDeviceIndex": 0,
      "Type": "SPIFlash",
    }
```

SPI controller driver says bound throughout the update process

```
root@s8030-bmc-30303035c0c1:/sys/bus/platform# ls /sys/bus/platform/drivers/spi-aspeed-smc/
1e620000.spi  1e630000.spi  bind          uevent        unbind
```

and SPI flash driver (spi-nor) is bound and then unbound after the
update process.

```
root@s8030-bmc-30303035c0c1:/sys/bus/platform# ls /sys/bus/spi/drivers/spi-nor/
bind    spi0.0  spi1.0  uevent  unbind
root@s8030-bmc-30303035c0c1:/sys/bus/platform# ls /sys/bus/spi/drivers/spi-nor/
bind    spi0.0  uevent  unbind
```

Change-Id: I874670f9fd27f6642359ea078e6e9db4c1b9e249
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/bios/spi_device.hpp b/bios/spi_device.hpp
index d05ab89..4a9e6fc 100644
--- a/bios/spi_device.hpp
+++ b/bios/spi_device.hpp
@@ -81,6 +81,7 @@
     // @returns          true on success
     sdbusplus::async::task<bool> unbindSPIFlash();
 
+    bool isSPIControllerBound();
     bool isSPIFlashBound();
 
     // @description preconditions: