OvmfPkg/QemuFwCfgLib: extend lib class header with more definitions

The last patch consists purely of code movement; going forward, we should
use a few more symbolic constants.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

OvmfPkg/Include/Library/QemuFwCfgLib.h

@@ -23,6 +23,13 @@
 //
 #define QEMU_FW_CFG_FNAME_SIZE 56
 
+//
+// If the following bit is set in the UINT32 fw_cfg revision / feature bitmap
+// -- read from key 0x0001 with the basic IO Port or MMIO method --, then the
+// DMA interface is available.
+//
+#define FW_CFG_F_DMA BIT1
+
 //
 // Macros for the FW_CFG_DMA_ACCESS.Control bitmap (in native encoding).
 //
@@ -30,6 +37,7 @@
 #define FW_CFG_DMA_CTL_READ   BIT1
 #define FW_CFG_DMA_CTL_SKIP   BIT2
 #define FW_CFG_DMA_CTL_SELECT BIT3
+#define FW_CFG_DMA_CTL_WRITE  BIT4
 
 typedef enum {
   QemuFwCfgItemSignature            = 0x0000,