hw/arm/Kconfig: Add missing dependency NPCM7XX -> SMBUS

hw/arm/Kconfig: Add missing dependency NPCM7XX -> SMBUS

The TYPE_NPCM7XX_SMBUS device model exposes an SMBus, but
this isn't advertised with proper Kconfig symbol, leading
to an early build failure when building NPCM7XX machines
standalone:

  The following clauses were found for AT24C

      config AT24C depends on I2C
      select AT24C if NPCM7XX

Fix by adding SMBUS to NPCM7XX.

Fixes: 94e77879395 ("hw/i2c: Implement NPCM7XX SMBus Module Single Mode")
Reviewed-by: Hao Wu <wuhaotsh@google.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210515173716.358295-4-philmd@redhat.com>