p4a : fix IRQ_PERI(x) modification mistake.

This issue was introduced by 'commit 481e517405cafac08ea78c0a52076af523b02c55'
p4a : fix mailbox modification mistake.

This issue was introducted by 'commit ba3a796a9995fe1fd6cfaed1800d1adbf1878929'
add two p4a bringup default configure files

p4abu_mailbox_defconfig : enable mailbox communication with CPU1.
p4abu_standalone_defconfig : CPU2 running only
cpu1 memory mapping don't care 'CONFIG_P4A_MAILBOX'