Fix #6686: Support passing Public Exponent when generating RSA key pair

Global Platform Internal API 1.0 is not accurate when describing
RSA key pair generation. It only indicates
    No parameter is required
This is why RSA key pair generation was always using 65537
as the public exponent.

Version 1.1 of the API is much more precise:
    No parameter is required.
    The TEE_ATTR_RSA_PUBLIC_EXPONENT attribute may be
    specified; if omitted, the default value is 65537.

This patch implements this requirement.

Change-Id: I9e4beb43d38d67b3d0cb9cbec505d8905239d8b0
Signed-off-by: Pascal Brand <pascal.brand@st.com>
Reviewed-on: https://gerrit.st.com/19866
Reviewed-by: Laurent GERARD <laurent.gerard@st.com>
Reviewed-by: Jean-Michel DELORME <jean-michel.delorme@st.com>