OvmfPkg: raise DXEFV size to 11 MB

OvmfPkg: raise DXEFV size to 11 MB

Almost exactly two years after commit 2f7b34b20842f, we've grown out the
10MB DXEFV:

> build -a IA32 -a X64 -p OvmfPkg/OvmfPkgIa32X64.dsc -b NOOPT -t GCC48 \
>   -D SMM_REQUIRE -D SECURE_BOOT_ENABLE -D TLS_ENABLE -D E1000_ENABLE \
>   -D HTTP_BOOT_ENABLE -D NETWORK_IP6_ENABLE
>
> [...]
>
> GenFv: ERROR 3000: Invalid
>   the required fv image size 0xa28d48 exceeds the set fv image size
>   0xa00000

Raise the DXEFV size to 11MB.

(For builds that don't need this DXEFV bump, I've checked the
FVMAIN_COMPACT increase stemming from the additional 1MB padding, using
NOOPT + GCC48 + FD_SIZE_2MB, and no other "-D" flags. In the IA32 build,
FVMAIN_COMPACT grows by 232 bytes. In the IA32X64 build, FVMAIN_COMPACT
shrinks by 64 bytes. In the X64 build, FVMAIN_COMPACT shrinks by 376
bytes.)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Gary Lin <glin@suse.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Gary Lin <glin@suse.com>