Corrected the register constraints for the PowerPC dcbt (Data Cache Block
Touch) instruction in Power10 kernel implementations. The dcbt instruction
has special behavior where if the first operand (RA) is r0, it uses the
value 0 instead of the register contents. Therefore, RA must use the "b"
constraint (any GPR except r0), while RB can use "r" (any GPR including r0).
Changes:
- Changed first operand constraint from "r" to "b" to exclude r0
- Changed second operand constraint from "b" to "r" for flexibility
This ensures correct prefetch behavior and compliance with PowerPC ISA
specifications, preventing potential issues where r0 might be incorrectly
used as the base address register.
Signed-off-by: Amrita H S <amritahs@linux.vnet.ibm.com>