ARC: Always use SWAPE instructions for __arch_swab32()

ARC: Always use SWAPE instructions for __arch_swab32()

Since commit 67a697e7576 ("ARC: retire ARC750 support") all supported
CPUs have the 'swape' instruction.

Always use the implementation of __arch_swabe() which uses 'swape'.
ARCH_USE_BUILTIN_BSWAP can not be used as that results on libcalls on
-mcpu=arc700.

As as side-effect, remove a leak of an internal kconfig symbol through
the UAPI headers.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/lkml/0ae2688a-5a22-405b-adaf-9b5ad712b245@app.fastmail.com/
Suggested-by: Vineet Gupta <vgupta@kernel.org>
Link: https://lore.kernel.org/lkml/a033a402-e3c5-4982-9fff-b6a4c55817ae@kernel.org/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>