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 <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

arch/x86/Kconfig

···
 	  For old smp systems that do not have proper acpi support. Newer systems
 	  (esp with 64bit cpus) with acpi support, MADT and DSDT will override it
 
-config GOLDFISH
-	def_bool y
-	depends on X86_GOLDFISH
-
 config X86_CPU_RESCTRL
 	bool "x86 CPU resource control support"
 	depends on X86 && (CPU_SUP_INTEL || CPU_SUP_AMD)

drivers/platform/goldfish/Kconfig

···
 menuconfig GOLDFISH
 	bool "Platform support for Goldfish virtual devices"
 	depends on HAS_IOMEM && HAS_DMA
+	default X86_GOLDFISH
 	help
 	  Say Y here to get to see options for the Goldfish virtual platform.
 	  This option alone does not add any kernel code.