MdeModulePkg/NvmExpressDxe: Fix some bugs

MdeModulePkg/NvmExpressDxe: Fix some bugs

1) The Queue size field in create I/O submission/completion queue cmds is 0-based. the current code is 1-based.
2) a typo on allocated memory page size. it's inconsistent that some places is using 4 pages, but a place is using 6 pages.
3) a typo on PRP/SGL mechanism judgment. should directly use Psdt field rather than Opc field.
4) some platforms may not support UINT64 width access on MMIO register. Fix it to use two 32-bit width access.

Signed-off-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Kinney Michael <michael.d.kinney@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14657 6f19259b-4bc3-4df7-8a09-765794883524