Blackfin: pull io funcs from linux

Some common code uses more of the io.h funcs than we currently provide, so
pull in all of the ones from the linux kernel.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/asm-blackfin/config-pre.h b/include/asm-blackfin/config-pre.h
index b1d3a94..1170a2a 100644
--- a/include/asm-blackfin/config-pre.h
+++ b/include/asm-blackfin/config-pre.h
@@ -71,4 +71,7 @@
 # define BFIN_BOOT_SPI_SSEL 1
 #endif
 
+/* We rarely use interrupts, so favor throughput over latency */
+#define CONFIG_BFIN_INS_LOWOVERHEAD
+
 #endif