[Maintenance] Declare PiHeader at a common place in ASM land

The longer you look at master.lib, the worse it looks.

Part of P0134, funded by [Anonymous].

libs/master.lib/graph_pi_free.asm

@@ -38,24 +38,6 @@
 ; Revision History:
 ;	93/11/24 Initial: grppifre.asm/master.lib 0.21
 
-PiHeader STRUC
-comment_offset	dw	?
-comment_segment	dw	?
-commentlen	dw	?
-_mode		db	?
-_n		db	?
-_m		db	?
-_plane		db	?
-_machine	db	4 dup (?)
-maexlen		dw	?
-maex_offset	dw	?
-maex_segment	dw	?
-_xsize		dw	?
-_ysize		dw	?
-_palette	db	48 dup (?)
-PiHeader ENDS
-
-
 func GRAPH_PI_FREE	; graph_pi_free() {
 	push	BP
 	mov	BP,SP

libs/master.lib/macros.inc

@@ -159,3 +159,24 @@ egc_setrop	macro mode_rop:rest
 	outw2	EGC_MODE_ROP_REG, mode_rop
 endm
 ; ---
+
+; .PI
+; ---
+
+PiHeader STRUC
+	comment_offset 	dw	?
+	comment_segment	dw	?
+	commentlen     	dw	?
+	PI_mode        	db	?
+	_n             	db	?
+	_m             	db	?
+	_plane         	db	?
+	_machine      	db	4 dup (?)
+	maexlen       	dw	?
+	maex_offset   	dw	?
+	maex_segment  	dw	?
+	_xsize        	dw	?
+	_ysize        	dw	?
+	_palette      	db	48 dup (?)
+PiHeader ENDS
+; ---