* include/grub/term.h (GRUB_TERM_LEFT, GRUB_TERM_RIGHT)
(GRUB_TERM_UP, GRUB_TERM_DOWN, GRUB_TERM_HOME, GRUB_TERM_END)
(GRUB_TERM_DC, GRUB_TERM_PPAGE, GRUB_TERM_NPAGE, GRUB_TERM_ESC)
(GRUB_TERM_TAB, GRUB_TERM_BACKSPACE): New macros.
* kern/i386/pc/startup.S: Include `<grub/term.h>'.
(translation_table): Replace hardcoded values with macros
provided by `<grub/term.h>'.
* term/i386/pc/at_keyboard.c: Include `<grub/term.h>'.
(keyboard_map): Correct/add a few values, with macros provided
by `<grub/term.h>'.
(keyboard_map_shift): Zero values that don't differ from their
`keyboard_map' equivalents.
(grub_console_checkkey): Optimize KEYBOARD_STATUS_CAPS_LOCK toggling.
Discard the second scan code that is always sent by Caps lock.
Only use `keyboard_map_shift' when it provides a non-zero value,
otherwise fallback to `keyboard_map'.