pc-bios: Add AST27x0 vBootrom

The boot ROM is a minimal implementation designed to load an AST27x0 boot image.
Its source code is available at:
https://github.com/google/vbootrom
Commit id: d6e3386709b3e49322a94ffadc2aaab9944ab77b
Build Information:
```
Build Date : Apr 29 2025 01:23:18
FW Version : git-d6e3386
```

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Nabih Estefan <nabihestefan@google.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Tested-by: Nabih Estefan <nabihestefan@google.com>
Link: https://lore.kernel.org/qemu-devel/20250429062822.1184920-2-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

MAINTAINERS

@@ -1174,6 +1174,7 @@ F: docs/system/arm/fby35.rst
 F: tests/*/*aspeed*
 F: tests/*/*ast2700*
 F: hw/arm/fby35.c
+F: pc-bios/ast27x0_bootrom.bin
 
 NRF51
 M: Joel Stanley <joel@jms.id.au>

pc-bios/README

@@ -89,6 +89,12 @@
   more features over time as needed. The source code is available at:
   https://github.com/google/vbootrom
 
+- ast27x0_bootrom.bin is a simplified, free (Apache 2.0) boot ROM for
+  ASPEED AST27x0 BMC SOC. It currently implements the bare minimum to
+  load, parse, initialize and run boot images stored in SPI flash, but may grow
+  more features over time as needed. The source code is available at:
+  https://github.com/google/vbootrom
+
 - hppa-firmware.img (32-bit) and hppa-firmware64.img (64-bit) are firmware
   files for the HP-PARISC (hppa) architecture.
   They are built form the SeaBIOS-hppa sources, which is a fork of SeaBIOS

pc-bios/meson.build

@@ -28,6 +28,7 @@ if unpack_edk2_blobs
 endif
 
 blobs = [
+  'ast27x0_bootrom.bin',
   'bios.bin',
   'bios-256k.bin',
   'bios-microvm.bin',