On systems with multiple SH per SE compute_static_thread_mgmt_se#
is split into independent masks, one for each SH, in the upper and
lower 16 bits.  We need to detect this and apply cu masking to each
SH.  The cu mask bits are assigned first to each SE, then to
alternate SHs, then finally to higher CU id.  This ensures that
the maximum number of SPIs are engaged as early as possible while
balancing CU assignment to each SH.

v2: Use max SH/SE rather than max SH in cu_per_sh.

v3: Fix comment blocks, ensure se_mask is initially zero filled,
    and correctly assign se.sh.cu positions to unset bits in cu_mask.
Signed-off-by: Sean Keely <Sean.Keely@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>