According to the hardware manual, when the Poll command is issued, the
byte returned by the I/O read is 1 in Bit 7 when there is an interrupt,
and the highest priority binary code in Bits 2:0. The current pic
simulation code is not implemented strictly according to the above
expression.

Fix the implementation of pic_poll_read(), set Bit 7 when there is an
interrupt.
Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Link: https://lore.kernel.org/r/20230419021924.1342184-1-alexjlzheng@tencent.comSigned-off-by: Sean Christopherson <seanjc@google.com>