drivers/intel/gma: Drop unused MAILBOXES_DESKTOP

MAILBOXES_DESKTOP is unused, and the IGD opregion spec makes no
distinction in the mailboxes supported between desktop and mobile
platforms. Rename MAILBOXES_MOBILE to IGD_MAILBOXES for consistency
with other mailbox variables and clean up the comment.

Change-Id: Ia06fe75702887aa6953bf17bd4bc14af4038bec5
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86279
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Author: MrChromebox

src/drivers/intel/gma/opregion.c

@@ -367,8 +367,8 @@ enum cb_err intel_gma_init_igd_opregion(void)
 	/* 8kb */
 	opregion->header.size = sizeof(igd_opregion_t) / 1024;
 
-	// FIXME We just assume we're mobile for now
-	opregion->header.mailboxes = MAILBOXES_MOBILE;
+	// Supported mailboxes
+	opregion->header.mailboxes = IGD_MAILBOXES;
 
 	// TODO Initialize Mailbox 1
 	opregion->mailbox1.clid = 1;

src/drivers/intel/gma/opregion.h

@@ -41,8 +41,7 @@ typedef struct {
 #define IGD_MBOX4	(1 << 3)
 #define IGD_MBOX5	(1 << 4)
 
-#define MAILBOXES_MOBILE  (IGD_MBOX1 | IGD_MBOX3 | IGD_MBOX4 | IGD_MBOX5)
-#define MAILBOXES_DESKTOP (IGD_MBOX2 | IGD_MBOX4)
+#define IGD_MAILBOXES	(IGD_MBOX1 | IGD_MBOX3 | IGD_MBOX4 | IGD_MBOX5)
 
 #define SBIOS_VERSION_SIZE 32