s390x/tcg: Introduce tcg_s390_vector_exception()

s390x/tcg: Introduce tcg_s390_vector_exception()

Handling is similar to data exceptions, however we can always store the
VXC into the lowore and the FPC:

z14 PoP, 6-20, "Vector-Exception Code"
    When a vector-processing exception causes a pro-
    gram interruption, a vector-exception code (VXC) is
    stored at location 147, and zeros are stored at loca-
    tions 144-146. The VXC is also placed in the DXC
    field of the floating-point-control (FPC) register if bit
    45 of control register 0 is one. When bit 45 of control
    register 0 is zero and bit 46 of control register 0 is
    one, the DXC field of the FPC register and the con-
    tents of storage at location 147 are unpredictable.

Signed-off-by: David Hildenbrand <david@redhat.com>