build/boot/roms_helper: shorten variable names

also: further reduce the number of arguments passed,
to certain functions as and when feasible, in cases
where those are global variables that never change.

the cbfstool argument in mkUbootRom wasn't even used.
that function was only using the global variable, which
again is only set once.

i also shortened a few messages, removed a few errant
line breaks and reduced sloccount by exactly 1 in main()
by re-arranging how the shift command is used.

it's mainly about shortening variable names, to then
reduce the number of line breaks, but it's a surgical
code size reduction in build/boot/roms.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/boot.sh

@@ -3,7 +3,7 @@
 # SPDX-FileCopyrightText: 2022 Ferass El Hafidi <vitali64pmemail@protonmail.com>
 # SPDX-FileCopyrightText: 2023 Leah Rowe <leah@libreboot.org>
 
-eval "$(setvars "" first board boards _displaymode _payload _keyboard_layout)"
+eval "$(setvars "" first board boards _displaymode _payload _keyboard)"
 
 main()
 {
@@ -16,21 +16,17 @@ main()
 
 	while [ $# -gt 0 ]; do
 		case ${1} in
-		-d)
-			_displaymode="${2}"
-			shift ;;
-		-p)
-			_payload="${2}"
-			shift ;;
-		-k)
-			_keyboard_layout="${2}"
-			shift ;;
+		-d) _displaymode="${2}" ;;
+		-p) _payload="${2}" ;;
+		-k) _keyboard="${2}" ;;
 		all)
-			first="all" ;;
+			first="all"
+			continue ;;
 		*)
-			boards="${1} ${boards}" ;;
+			boards="${1} ${boards}"
+			continue ;;
 		esac
-		shift
+		shift 2
 	done
 
 	handle_targets