arch: remove blackfin port

The Analog Devices Blackfin port was added in 2007 and was rather
active for a while, but all work on it has come to a standstill
over time, as Analog have changed their product line-up.

Aaron Wu confirmed that the architecture port is no longer relevant,
and multiple people suggested removing blackfin independently because
of some of its oddities like a non-working SMP port, and the amount of
duplication between the chip variants, which cause extra work when
doing cross-architecture changes.

Link: https://docs.blackfin.uclinux.org/
Acked-by: Aaron Wu <Aaron.Wu@analog.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Cc: Steven Miao <realmz6@gmail.com>
Cc: Mike Frysinger <vapier@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/admin-guide/kernel-parameters.rst

@@ -89,7 +89,6 @@ parameter is applicable::
 	APM	Advanced Power Management support is enabled.
 	ARM	ARM architecture is enabled.
 	AX25	Appropriate AX.25 support is enabled.
-	BLACKFIN Blackfin architecture is enabled.
 	CLK	Common clock infrastructure is enabled.
 	CMA	Contiguous Memory Area support is enabled.
 	DRM	Direct Rendering Management support is enabled.

Documentation/admin-guide/kernel-parameters.txt

@@ -1025,7 +1025,7 @@
 			address. The serial port must already be setup
 			and configured. Options are not yet supported.
 
-	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k,S390]
+	earlyprintk=	[X86,SH,ARM,M68k,S390]
 			earlyprintk=vga
 			earlyprintk=efi
 			earlyprintk=sclp