ARM: s3c64xx: fix pm-debug compilation

I got one randconfig build that failed to compile plat-samsung/pm-debug.c
on s3c64xx:

In file included from arch/arm/plat-samsung/pm-debug.c:27:0:
arch/arm/mach-s3c64xx/include/mach/pm-core.h: In function 's3c_pm_debug_init_uart':
arch/arm/mach-s3c64xx/include/mach/pm-core.h:25:25: error: 'S3C_VA_SYS' undeclared (first use in this function)
  u32 tmp = __raw_readl(S3C_PCLK_GATE);
arch/arm/mach-s3c64xx/include/mach/pm-core.h:25:25: note: each undeclared identifier is reported only once for each function it appears in
arch/arm/mach-s3c64xx/include/mach/pm-core.h:39:2: error: implicit declaration of function 'udelay' [-Werror=implicit-function-declaration]
  udelay(10);

I have not investigated why this does not show up much more often, I
guess the headers are usually included from elsewhere, but adding
explicit #include statements is an obvious fix.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>