ice: rename ice_write_* functions to ice_pack_ctx_*

In ice_common.c there are 4 functions used for converting the unpacked
software Tx and Rx context structure data into the packed format used by
hardware. These functions have extremely generic names:

 * ice_write_byte
 * ice_write_word
 * ice_write_dword
 * ice_write_qword

When I saw these function names my first thought was "write what? to
where?". Understanding what these functions do requires looking at the
implementation details. The functions take bits from an unpacked structure
and copy them into the packed layout used by hardware.

As part of live migration, we will want functions which perform the inverse
operation of reading bits from the packed layout and copying them into the
unpacked format. Naming these as "ice_read_byte", etc would be very
confusing since they appear to write data.

In preparation for adding this new inverse operation, rename the existing
functions to use the prefix "ice_pack_ctx_". This makes it clear that they
perform the bit packing while copying from the unpacked software context
structure to the packed hardware context.

The inverse operations can then neatly be named ice_unpack_ctx_*, clearly
indicating they perform the bit unpacking while copying from the packed
hardware context to the unpacked software context structure.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>