loader: Fix 0 vs 1 confusion for column numbers

In two places we use '0' for a column number. However, the upper left
hand corner of the screen is 1, 1. Fix those two confusions. Also, fix
a comment that flipped the coordinates in a comment (I'm used to the
vt100 convention where it's row, column (eg y, x)) and didn't notice
the rest of the code uses x, y.

Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D46777

stand/lua/menu.lua

@@ -556,9 +556,9 @@ function menu.autoboot(delay)
 			else
 				-- Erase autoboot msg.  While real VT100s
 				-- wouldn't scroll when receiving a char with
-				-- the cursor at (24, 79), bad emulators do.
+				-- the cursor at (79, 24), bad emulators do.
 				-- Avoid the issue by stopping at 79.
-				screen.setcursor(0, y)
+				screen.setcursor(1, y)
 				printc(string.rep(" ", 79))
 				screen.defcursor()
 				return ch

stand/lua/screen.lua

@@ -32,7 +32,7 @@ local core = require("core")
 local screen = {}
 
 -- Module exports
-screen.default_x = 0
+screen.default_x = 1
 screen.default_y = 25
 
 function screen.clear()