Blackfin arch: add functions for converting between sclks and usecs

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

diff --git a/include/asm-blackfin/bfin-global.h b/include/asm-blackfin/bfin-global.h
index a006353a4..14cb8d3 100644
--- a/include/asm-blackfin/bfin-global.h
+++ b/include/asm-blackfin/bfin-global.h
@@ -47,6 +47,8 @@
 
 extern unsigned long get_cclk(void);
 extern unsigned long get_sclk(void);
+extern unsigned long sclk_to_usecs(unsigned long sclk);
+extern unsigned long usecs_to_sclk(unsigned long usecs);
 
 extern void dump_thread(struct pt_regs *regs, struct user *dump);
 extern void dump_bfin_regs(struct pt_regs *fp, void *retaddr);