defaults.mk: default KEY_SIZE to 2048 in case of RSA algorithm

According to the documentation [1], KEY_SIZE defaults to 2048 when RSA
algorithm is chosen, so set this value on the make's defaults file.

[1] https://trustedfirmware-a.readthedocs.io/en/latest/getting_started/build-options.html

Change-Id: I030f98363198a752bc0dd03528f748de527d48d8
Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
1 file changed