riscv: Move high_memory initialization to setup_bootmem

riscv: Move high_memory initialization to setup_bootmem

high_memory used to be initialized in mem_init, way after setup_bootmem.
But a call to dma_contiguous_reserve in this function gives rise to the
below warning because high_memory is equal to 0 and is used at the very
beginning at cma_declare_contiguous_nid.

It went unnoticed since the move of the kasan region redefined
KERN_VIRT_SIZE so that it does not encompass -1 anymore.

Fix this by initializing high_memory in setup_bootmem.

------------[ cut here ]------------
virt_to_phys used for non-linear address: ffffffffffffffff (0xffffffffffffffff)
WARNING: CPU: 0 PID: 0 at arch/riscv/mm/physaddr.c:14 __virt_to_phys+0xac/0x1b8
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 5.17.0-rc1-00007-ga68b89289e26 #27
Hardware name: riscv-virtio,qemu (DT)
epc : __virt_to_phys+0xac/0x1b8
 ra : __virt_to_phys+0xac/0x1b8
epc : ffffffff80014922 ra : ffffffff80014922 sp : ffffffff84a03c30
 gp : ffffffff85866c80 tp : ffffffff84a3f180 t0 : ffffffff86bce657
 t1 : fffffffef09406e8 t2 : 0000000000000000 s0 : ffffffff84a03c70
 s1 : ffffffffffffffff a0 : 000000000000004f a1 : 00000000000f0000
 a2 : 0000000000000002 a3 : ffffffff8011f408 a4 : 0000000000000000
 a5 : 0000000000000000 a6 : 0000000000f00000 a7 : ffffffff84a03747
 s2 : ffffffd800000000 s3 : ffffffff86ef4000 s4 : ffffffff8467f828
 s5 : fffffff800000000 s6 : 8000000000006800 s7 : 0000000000000000
 s8 : 0000000480000000 s9 : 0000000080038ea0 s10: 0000000000000000
 s11: ffffffffffffffff t3 : ffffffff84a035c0 t4 : fffffffef09406e8
 t5 : fffffffef09406e9 t6 : ffffffff84a03758
status: 0000000000000100 badaddr: 0000000000000000 cause: 0000000000000003
[<ffffffff8322ef4c>] cma_declare_contiguous_nid+0xf2/0x64a
[<ffffffff83212a58>] dma_contiguous_reserve_area+0x46/0xb4
[<ffffffff83212c3a>] dma_contiguous_reserve+0x174/0x18e
[<ffffffff83208fc2>] paging_init+0x12c/0x35e
[<ffffffff83206bd2>] setup_arch+0x120/0x74e
[<ffffffff83201416>] start_kernel+0xce/0x68c
irq event stamp: 0
hardirqs last  enabled at (0): [<0000000000000000>] 0x0
hardirqs last disabled at (0): [<0000000000000000>] 0x0
softirqs last  enabled at (0): [<0000000000000000>] 0x0
softirqs last disabled at (0): [<0000000000000000>] 0x0
---[ end trace 0000000000000000 ]---

Fixes: f7ae02333d13 ("riscv: Move KASAN mapping next to the kernel mapping")
Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>