ARM: zynq/zynqmp: Use the default CONFIG_BOOTDELAY=2

Based on:
"ARM: uniphier: use the default CONFIG_BOOTDELAY=2"
(sha1: 7c8ef0fe)

"I do not insist on CONFIG_BOOTDELAY=3. The default value in Kconfig,
CONFIG_BOOTDELAY=2, is just fine for these boards."

Reported-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>