* config/avr/avr.c (ashlhi3_out, ashlsi3_out, ashrhi3_out,
ashrsi3_out, lshrhi3_out, lshrsi3_out): Optimize more cases
with known shift count.
* config/avr/avr.md (ashlsi3, ashrsi3, lshrsi3):
New alternative for shift count 2 with no scratch register.
(ashlhi3, ashlsi3): Change "cc" attribute from "clobber" to
"set_n" for shift counts 1 and 2.
From-SVN: r36685
