Implement atomic_load_acq_16

[br]

Summary

• Implement atomic_load_acq_16(), atomic_store_rel_16(). One of these needed for bhyve pci emulation.
• Group 16-bit functions similarly to 32 and 64.

Test Plan

bhyve pass

[mhorne]

sys/riscv/include/atomic.h

116–117

These two lines should be grouped with the other #defines below.

122

?

[br]

sys/riscv/include/atomic.h

116–117

should we use same grouping as for 32 / 64 ? cmpset/fcmpset seem to go before acquire/release declarations in 32, 64 variants

122

needed by sys/_atomic_subword.h as it checks if macro defined

[mhorne]

sys/riscv/include/atomic.h

116–117

You are right, it is fine as-is.