intel-iommu: check definitions of CSRs and change the capability registers

Check and correct the definitions of all the CSRs in intel_iommu.c, including
the default values, bit semantics and so on.
Change the value of the Capability Register and Extended Capability Register
to make only the simplest functionality remain.
Add function define_quad_wo() for defining the write-only property of 64-bit.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: fixup coding style

Fixup coding style issue in hw/i386/intel_iommu.c and
include/hw/i386/intel_iommu.h.

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: add basic responses to CSRs accesses

Add basic responses to some basic CSRs accesses. Logics are not intact yet.
Now Linux seems to be able to initialize the VT-d

Signed-off-by: Le Tan <tamlokveer@gmail.com>