target/ppc: Fix BookE debug interrupt generation

target/ppc: Fix BookE debug interrupt generation

Per E500 core reference manual [1], chapter 8.4.4 "Branch Taken Debug
Event" and chapter 8.4.5 "Instruction Complete Debug Event":

  "A branch taken debug event occurs if both MSR[DE] and DBCR0[BRT]
  are set ... Branch taken debug events are not recognized if MSR[DE]
  is cleared when the branch instruction executes."

  "An instruction complete debug event occurs when any instruction
  completes execution so long as MSR[DE] and DBCR0[ICMP] are both
  set ... Instruction complete debug events are not recognized if
  MSR[DE] is cleared at the time of the instruction execution."

Current codes do not check MSR.DE bit before setting HFLAGS_SE and
HFLAGS_BE flag, which would cause the immediate debug interrupt to
be generated, e.g.: when DBCR0.ICMP bit is set by guest software
and MSR.DE is not set.

[1] https://www.nxp.com/docs/en/reference-manual/E500CORERM.pdf

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Lucas Mateus Castro <lucas.araujo@eldorado.org.br>
Message-Id: <20220421011729.1148727-1-bmeng.cn@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>