Update seabios submodule to 1.7.4

Not that many changes as we already have a git snapshot pretty close
to final 1.7.4 in the tree.  Most notably change is the vgabios change
which fixes the windows guest regression.

Full git shortlog:

Gerd Hoffmann (2):
      run qemu_cfg_e820 only for CONFIG_QEMU=y
      change boot order load log level

Kevin O'Connor (10):
      Minor - move sgdt/lgdt macros from stacks.c to x86.h.
      Separate out sec32init sections even when not doing code relocation.
      floppy: Fix incorrect LBA to CHS translation.
      floppy: Fix accesses to DOR register.
      vgabios: Avoid memory references via %esp register in vgabios.
      Small improvements to irqentry_extrastack assembler.
      floppy: Encode command and flags into single value in floppy pio code.
      On disk format request, verify cylinders and pass to driver.
      floppy: Implement cylinder seeking when accessing a different cylinder.
      coreboot: Make sure to print the SeaBIOS version in cbmem debug output.

Kyösti Mälkki (1):
      Fix CBMEM console overflow

diff --git a/roms/seabios b/roms/seabios
index 31b8b4e..96917a8 160000 (submodule)
--- a/roms/seabios
+++ b/roms/seabios
@@ -1 +1 @@
-Subproject commit 31b8b4eea9d9ad58a73b22a6060d3ac1c419c26d
+Subproject commit 96917a8ed761f017fc8c72ba3b9181fbac03ac59