DPC++ daily 2021-10-11

[ESIMD] Refactor esimd intrinsic mapping to BE intrinsics. (#4720)

* [ESIMD] Refactor esimd intrinsic mapping to BE intrinsics.

This patch
- makes names and parameter lists of __esimd* intrinsics match their
  @llvm.genx counterparts. The benefits are:
  * this removes the extra logical translation layer between __esimd* and
    @llvm.genx thus simplifying overall user-level esimd intrinsic translation
  * allows to reuse lots of functionality between SLM and surface memory
    accesses
- moves some of the translations and argument setting (like accessor field to
  surface index, setting scale) from LowerESIMD.cpp to the ESIMD headers, which
  simplifies code base.
- for all memory intrinsics moves host and device implementations to the same
  intrinsic function prototype separating them via __SYCL_DEVICE_ONLY__ macro
  thus avoiding duplication of the prototypes
- removes certain redundant __esimd* intrinsics, such as SLM memory accesses
  (which are normal surface accesses with special surface index 254), and
  __esimd_reduced_fmax,... which have the same functionality as usual fmax,...

This is also a preparatory step for fixing SLM memory accesses (revising vector
lengths, element types restirictions)

Signed-off-by: Konstantin S Bobrovsky <[email protected]>