platform: goldfish: move the separate 'default' propery for CONFIG_GOLDFISH

platform: goldfish: move the separate 'default' propery for CONFIG_GOLDFISH

Currently, there are two entries for CONFIG_GOLDFISH.

In arch/x86/Kconfig:

  config GOLDFISH
          def_bool y
          depends on X86_GOLDFISH

In drivers/platform/goldfish/Kconfig:

  menuconfig GOLDFISH
          bool "Platform support for Goldfish virtual devices"
          depends on HAS_IOMEM && HAS_DMA

While Kconfig allows multiple entries, it generally leads to tricky
code.

Prior to commit bd2f348db503 ("goldfish: refactor goldfish platform
configs"), CONFIG_GOLDFISH was an alias of CONFIG_X86_GOLDFISH.

After the mentioned commit added the second entry with a user prompt,
the former provides the 'default' property that is effective only when
X86_GOLDFISH=y.

Merge them tegether to clarify how it has worked in the past 8 years.

Cc: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240204081004.33871-1-masahiroy@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>