ArmVirtPkg/ArmVirtXen: don't set PcdTerminalTypeGuidBuffer

According to the

  PCDs not used by modules or in conditional directives

sections of all the build reports for

  {AARCH64,ARM} x {Xen} x {DEBUG,NOOPT,RELEASE} x {feat-0,feat-1}

(12 builds in total), the PCD is not used in any of those builds.

Restrict the setting to the ArmVirtQemu and ArmVirtQemuKernel platforms.
Restrict the TTY_TERMINAL define similarly.

("feat-1" stands for "-D HTTP_BOOT_ENABLE -D NETWORK_IP6_ENABLE -D
SECURE_BOOT_ENABLE -D TTY_TERMINAL", while "feat-0" stands for "".)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Julien Grall <julien.grall@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

ArmVirtPkg/ArmVirtQemuKernel.dsc

@@ -33,6 +33,7 @@
   # Defines for default states.  These can be changed on the command line.
   # -D FLAG=VALUE
   #
+  DEFINE TTY_TERMINAL            = FALSE
   DEFINE SECURE_BOOT_ENABLE      = FALSE
   DEFINE NETWORK_IP6_ENABLE      = FALSE
   DEFINE HTTP_BOOT_ENABLE        = FALSE
@@ -115,6 +116,8 @@
   ## 0-PCANSI, 1-VT100, 2-VT00+, 3-UTF8, 4-TTYTERM
 !if $(TTY_TERMINAL) == TRUE
   gEfiMdePkgTokenSpaceGuid.PcdDefaultTerminalType|4
+  # Set terminal type to TtyTerm, the value encoded is EFI_TTY_TERM_GUID
+  gArmVirtTokenSpaceGuid.PcdTerminalTypeGuidBuffer|{0x80, 0x6d, 0x91, 0x7d, 0xb1, 0x5b, 0x8c, 0x45, 0xa4, 0x8f, 0xe2, 0x5f, 0xdd, 0x51, 0xef, 0x94}
 !else
   gEfiMdePkgTokenSpaceGuid.PcdDefaultTerminalType|1
 !endif