ARM: shmobile: apmu: Allow booting secondary CPU cores in debug mode

Now debug resource reset is handled properly, allow booting secondary
CPU cores when hardware debug mode is enabled (MD21=1) on SoCs using the
"renesas,apmu" enable method.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Hiep Cao Minh <cm-hiep@jinso.co.jp>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>