nvme: added 'readl2ptbl' driver option

For testing purposes, allowing device initialization with as fresh
L2P table is desirable, as it permits
nvme: refactoring for consistent use of variable identifier 'ln'

Code used 'ln' to refer to both 'LnvmCtrl' and 'LnvmIdCtrl' -
now 'ln' exclusively refers to 'LnvmCtrl' and 'ln_id' to
'LnvmIdCtrl'.
nvme: cleaned up spba error handling

spba error handling set the wrong error bit (NVME_LBA_RANGE) for
an invalid physical block address. Also, the call to the error
page pointed to the wrong variable as the offending value.
nvme: cleaned up LNVM erase functions

Fixed range checking, declared a LNVM data management cmd struct
and used it instead - conveys that the command operates directly
on the physical address space.