od: rs90: Set page size to 4k

This makes the OS and applications a lot more RAM efficient:

1. Reduces OS overhead by 3.5 MiB.
2. Reduces RAM usage of applications (amount varies).

This comes at small performance cost,
<1 FPS in the emulators and ports that I've tested.

Measuring `MemAvailable` and `Slab` with just "Terminal" running:

Before:

    MemAvailable:       9760 kB
    Slab:               6816 kB

After:

    MemAvailable:      13812 kB
    Slab:               5904 kB

DevilutionX now loads the dungeon (without audio)
and the FPS is unchanged.

Signed-off-by: Gleb Mazovetskiy <[email protected]>

board/opendingux/rs90/linux_defconfig

@@ -27,7 +27,7 @@ CONFIG_PROFILING=y
 CONFIG_MACH_INGENIC_SOC=y
 CONFIG_JZ4740_RS90=y
 CONFIG_ZBOOT_LOAD_ADDRESS=0x81000000
-CONFIG_PAGE_SIZE_16KB=y
+CONFIG_PAGE_SIZE_4KB=y
 CONFIG_ARCH_FORCE_MAX_ORDER=7
 # CONFIG_MIPS_FP_SUPPORT is not set
 CONFIG_HZ_24=y