[AMDGPU] Rename amdgcn_wwm to amdgcn_strict_wwm

 * Introduce the new intrinsic amdgcn_strict_wwm
 * Deprecate the old intrinsic amdgcn_wwm

The change is done for consistency as the "strict"
prefix will become an important, distinguishing factor
between amdgcn_wqm and amdgcn_strictwqm in the future.

The "strict" prefix indicates that inactive lanes do not
take part in control flow, specifically an inactive lane
enabled by a strict mode will always be enabled irrespective
of control flow decisions.

The amdgcn_wwm will be removed, but doing so in two steps
gives users time to switch to the new name at their own pace.

Reviewed By: critson

Differential Revision: https://reviews.llvm.org/D96257