[rfa/arm] Remove HOST_BYTE_ORDER from arm-tdep.c

[Andrew Cagney]

Hello,

The attatched patch eliminates the use of HOST_BYTE_ORDER in the file 
arm-tdep.c.  In the process I think it rewrites the float->double code 
in a more portable way.

Given I don't have an ARM toolchain handy it still needs testing :-/

	Andrew