sparc: remove obsolete config ARCH_ATU

Before consolidation of commit 4965a68780c5 ("arch: define the
ARCH_DMA_ADDR_T_64BIT config symbol in lib/Kconfig"), the config ARCH_ATU
was used to control the state of the config ARCH_DMA_ADDR_T_64BIT. After
this consolidation, the config ARCH_ATU has been without use and effect.

Remove this obsolete config.

Signed-off-by: Lukas Bulwahn <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Andreas Larsson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/sparc/Kconfig

···
 config CPU_BIG_ENDIAN
 	def_bool y
 
-config ARCH_ATU
-	bool
-	default y if SPARC64
-
 config STACKTRACE_SUPPORT
 	bool
 	default y if SPARC64