MFC: rp.c 1.69, 1.71, 1.72; rp_isa.c 1.8; rp_pci.c 1.12; rpreg.h 1.8;

MFC: rp.c 1.69, 1.71, 1.72; rp_isa.c 1.8; rp_pci.c 1.12; rpreg.h 1.8;
     rpvar.h 1.9, 1.10

- We know it is called rpclose() so call it directly.
- Fix -Wundef from compiling the amd64 LINT.
- Make rp(4) 64-bit- and endian-clean as well as work on strict alignment
  archs.
- Instead of bus_space_{read,write}*(rman_get_bustag(), rman_get_bushandle())
  use bus_{read,write}*(). Unlike in 7.0-CURRENT, this has no other benefit
  than diff reduction with HEAD.