monitor: rename keyname '<' to 'less'

monitor: rename keyname '<' to 'less'

There are many maps of keycode 0x56 in pc-bios/keymaps/*
  pc-bios/keymaps/common:less 0x56
  pc-bios/keymaps/common:greater 0x56 shift
  pc-bios/keymaps/common:bar 0x56 altgr
  pc-bios/keymaps/common:brokenbar 0x56 shift altgr

This patch just renamed '<' to 'less', QAPI might add new
variable by adding a prefix to keyname, '$PREFIX_<' is not
available, '$PREFIX_less' is ok.

For compatibility, convert user inputted '<' to 'less'.

Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>