fix(xilinx): resolve integer handling issue

OEN Number 48 to 63 is for Trusted App and OS.
GET_SMC_OEN limits the return value of OEN number to 63 by bitwise AND
operation with 0x3F. Thus the upper limit check for OEN value returned
by GET_SMC_OEN is not required.
Removing the upper limit check for the OEN value returned by GET_SMC_OEN
resolves integer handling issue CONSTANT_EXPRESSION_RESULT

Signed-off-by: Akshay Belsare <akshay.belsare@amd.com>
Change-Id: Ie04a4e2fb7cc85ec6055a5662736a805a89f7085