swtpm_cert: Use keychoice variable to disallow conflicting CLI options Introduce a 'keychoice' variable and set it when the user provides an option for a particular type of key, such as the modulus or exponent for an RSA key or the x and y parameters for an EC key. Check that no conflicting parameters are provided. Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>