refactor: define exception_handler.c for el0

The test/common/exception_handler.c file was implemented
for the EL1 partitions, as it does system register accesses
that belong to EL1.

This patch creates a new souce file to be used for EL0,
paritions separating both implementations.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I8ee75e5ff8e6bf61446b434732d5a8c78a9fbe63
45 files changed