RFR(T): 8223395: PPC64: Improve comments in the JVM signal handler to match ISA text

[Gustavo Romero]

Hi,

Could the following trivial fix be reviewed please?

Bug    : https://bugs.openjdk.java.net/browse/JDK-8223395
Webrev : http://cr.openjdk.java.net/~gromero/8223395/v1/

It improves the text about Data and Instruction interrupts in the JVM signal
handler and also cleans up the "os_trap_1" note.

Thank you.

Best regards,
Gustavo