revert(zynqmp): remove EM SMC handler

EM support was out of SMC SIP range that's why has been moved to SIP
range 0x3000 by commit acbae399 ("fix(zynqmp): move EM SMC range
to SIP range").
But after another investigation was found that this interface has no
user in any our SW and likely never adopted by anybody else. That's
why simply remove it. If there is any user it can be added back but
as TF-A size is challenging removing unused code is very welcome.
Origin code was added by commit 504925f9 ("xilinx: zynqmp: Add
support for Error Management").

Change-Id: I2d9222d7dde507400893e06f7f12e1713ce6bc9a
Signed-off-by: Michal Simek <michal.simek@amd.com>