target-arm: Extend FP checks to use an EL

Extend the ARM disassemble context to take a target exception EL instead of a
boolean enable. This change reverses the polarity of the check making a value
of 0 indicate floating point enabled (no exception).

Signed-off-by: Greg Bellows <greg.bellows@linaro.org>
[PMM: Use a common TB flag field for AArch32 and AArch64;
 CPTR_EL2 exists in v7; CPTR_EL2 should trap for EL2 accesses;
 CPTR_EL2 should not trap for secure accesses; CPTR_EL3
 should trap for EL3 accesses; CPACR traps for secure
 accesses should trap to EL3 if EL3 is AArch32]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
