soc/amd/common/data_fabric_helper: add comment about cfg_inst_acc_en

Since all indirect data fabric register accesses will be non-broadcast
accesses that target a specific data fabric instance, the
cfg_inst_acc_en bit in the DF_FICAA_BIOS register will always be set
since that makes the indirect access target only a specific data fabric
instance.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I9aff01750c2c1e3506141b3ed293a980a64f8fac
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76885
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

src/soc/amd/common/block/data_fabric/data_fabric_helper.c

@@ -13,7 +13,7 @@
 
 static void data_fabric_set_indirect_address(uint8_t func, uint16_t reg, uint8_t instance_id)
 {
-	union df_ficaa ficaa = { .cfg_inst_acc_en = 1 };
+	union df_ficaa ficaa = { .cfg_inst_acc_en = 1 }; /* target only specific instance */
 	/* convert register address to 32-bit register number */
 	ficaa.reg_num = reg >> 2;
 	ficaa.func_num = func;