Disable interrupts while manipulating port mapping control on MSP430

Disable interrupts while manipulating port mapping control, since the port
mapping will forever be read only if the configuration takes more than 32
(assembler) instructions, this is specified in
http://www.ti.com/lit/ug/slau208n/slau208n.pdf, section "13.2 Port Mapping Controller Operation", page 426

Use PMAPKEYID instead of PMAPPWD, which is deprecated, when setting port mapping password.