meson: use b_staticpic=false for meson >=0.56.0

Meson 0.56.0 correctly builds non-PIC static libraries with -fPIE if
b_pie=true.  We do not have to pass b_staticpic=true if PIE is requested
if Meson is new-enough, which improves performance.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>