lmb: Fix adjacent region merge in lmb_add_region_flags()

In case a new region is adjacent to a previous region with
similar flag, this region is merged with its predecessor, but no
check are done if this new added region is overlapping another region
present in lmb (see reserved[3] which overlaps reserved[4]).

This occurs when the LMB [0xdaafd000-0xddb18000] is added and overlaps
the LMB [0xdbaf4380-0xddffffff].

Call lmb_overlaps_region() before merging the new region with the
adjacent region already present in lmb.

In case of adjacent region found, code is 90% similar in case
adjacent region is located before/after the new region.
Factorize adjacent region management in lmb_add_region_flags().

Issue reproduced on STM32MP157-DK2 with SCMI DT, bdinfo command's output
shows:

before this patch:
...
lmb_dump_all:
 memory.cnt = 0x1 / max = 0x2
 memory[0]      [0xc0000000-0xdfffffff], 0x20000000 bytes flags: 0
 reserved.cnt = 0x5 / max = 0x10
 reserved[0]    [0x10000000-0x10045fff], 0x00046000 bytes flags: 4
 reserved[1]    [0x30000000-0x3003ffff], 0x00040000 bytes flags: 4
 reserved[2]    [0x38000000-0x3800ffff], 0x00010000 bytes flags: 4
 reserved[3]    [0xdaadf000-0xdfffffff], 0x05521000 bytes flags: 0
 reserved[4]    [0xde000000-0xdfffffff], 0x02000000 bytes flags: 4
...

after this patch:

...
lmb_dump_all:
 memory.cnt = 0x1 / max = 0x2
 memory[0]      [0xc0000000-0xdfffffff], 0x20000000 bytes flags: 0
 reserved.cnt = 0x6 / max = 0x10
 reserved[0]    [0x10000000-0x10045fff], 0x00046000 bytes flags: 4
 reserved[1]    [0x30000000-0x3003ffff], 0x00040000 bytes flags: 4
 reserved[2]    [0x38000000-0x3800ffff], 0x00010000 bytes flags: 4
 reserved[3]    [0xdaadf000-0xdaaf7fff], 0x00019000 bytes flags: 0
 reserved[4]    [0xdbaf4380-0xddffffff], 0x0250bc80 bytes flags: 0
 reserved[5]    [0xde000000-0xdfffffff], 0x02000000 bytes flags: 4
...

Fixes: 4ed6552f ("[new uImage] Introduce lmb from linux kernel for memory mgmt of boot images")

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>