RFR 8248870: AARCH64: I2L conversions can be skipped for small positive masked values

[Boris Ulasevich]

Hi,

Please review the change to skip i2l conversion after the mask:

http://cr.openjdk.java.net/~bulasevich/8248870/webrev.00
http://bugs.openjdk.java.net/browse/JDK-8248870

With the change the micro-benchmark gets 11.082->7.520 ns/op
performance improvement. Tested with jtreg.

thanks,
Boris